For an industrial power supply (AC to DC, installed in a control cabinet or machine), first calculate the load (output voltage and current, plus about 25% margin), then check how much it can still deliver when the cabinet is hot (derating), next confirm the input range and form factor, and after that look at protection, redundancy, and safety certification. The rated current on the specification sheet should be compared on the basis of “how much it can still deliver at the site’s upper temperature limit,” not the number on the nameplate. This article is written for people choosing a DC power supply for PLCs, sensors, control panels, or machines; computer power supplies and phone chargers are out of scope. It is divided into 4 stages:
Stage ① | Load and output: the equipment to be powered, voltage, current, and the surge at power-on.
Stage ② | Power margin and temperature: how much margin to leave, and how much it can still deliver when the cabinet is hot.
Stage ③ | Input and form factor: input voltage range, inrush current at power-on, DIN rail, enclosed, rack-mount, or plug-in.
Stage ④ | Protection, redundancy, and certification: short-circuit and overload protection, parallel redundancy, safety standards.
For how to measure and manage the ambient temperature of cabinets and the plant, see “How Tightly to Control Plant Temperature and Humidity: Which Conditions Matter for Solder Paste, Moisture-Sensitive Parts, and ESD — 5 Stages from Setting Windows to Audits“; this article starts from “you already know you need an AC-to-DC power supply.” Each stage below covers: how to do it, what public sources say, and how Jiahon can help; sources, exceptions, and synthesis are in the “Notes” at the end.
① Load and output
Equipment to be powered
Write down voltage and current unit by unit
Sum current per voltage
First total the current for each voltage
Surge at power-on
Check for a peak current rating
When this step is done, you should have
Total current and surge for each voltage
▶
② Power margin and temperature
Leave margin
Add another quarter to the total current
Check the derating curve
Compare using values at cabinet high temperature
Fans and mounting orientation
The datasheet gives separate derating
When this step is done, you should have
A specification that is still enough when hot
▶
③ Input and form factor
Input voltage range
Covers site voltage and phases
Inrush current at power-on
Adds up when several start together
Form factor
DIN rail, enclosed, rack, plug-in
When this step is done, you should have
Input and form factor confirmed
▶
④ Protection, redundancy, and certification
Protection
Short circuit, overload, overvoltage, overtemperature
Signals and redundancy
DC OK, parallel, isolation
Safety certification
Check against equipment and customer requirements
When this step is done, you should have
A list of protection and certification
Figure 1 The four stages of power supply selection: load and output, power margin and temperature, input and form factor, protection, redundancy, and certification (schematic, not to scale)
Stage ①: Load and Output — First Work Out How Much Power Is Needed
How to do it:
First list all the equipment to be connected, write down the voltage and current each unit needs, and add up the current for each voltage.
Most output voltages are 24 V; there are also 5 V, 12 V, 15 V, 48 V, or models with several outputs at once. For the same 100 W, 12 V needs about 8.3 A while 24 V needs only about 4.2 A; higher current means thicker wire and greater voltage drop on the line, so for long cable runs, give priority to the higher voltage (this article’s own synthesis).
Current at power-on: contactors, solenoid valves, and loads with large capacitors can draw many times their normal current at power-on. Check whether the power supply states a “peak current it can deliver for a short time”; otherwise it may trip its protection at power-on and restart repeatedly.
Some output voltages can be fine-tuned (commonly about ±10%), which can be used to compensate for voltage drop on long lines.
What public sources say: A power supply distributor’s public guide says: for a 100 W load, 12 V is about 8.3 A and 24 V about 4.2 A; 12 V needs thicker wire and has greater voltage drop, while 24 V wire can be thinner and run longer; most good-quality power supplies can be adjusted by about ±10% to compensate for voltage drop on long lines; contactors, solenoid valves, and capacitive loads draw many times their steady-state current at power-on, and it recommends choosing a model with a “clearly stated peak power range” so it does not go into hiccup mode. A sponsored article by an electronic components distributor published in electronics media (July 2026) says: 24 V is common, along with 5 V, 12 V, 15 V, and 48 V; add up the power consumption of all equipment (including communication modules, displays, and relays), then leave margin for power-on current and expansion (Notes Table 1).
How Jiahon can help:
Their output specifications all differ, and they are listed below as written on the product pages. For anything not stated on the product page, please inquire.
DC Power Supply: input AC 100–240 V; output DC 24 V / 10 A (the product page states 240 W); voltage stability ±1%. The product page text says “two models,” but the specification table lists only this one; the specifications of the other model are not stated on the product page, so please inquire.
DC Power Supply (Ultra-Wide Input Industrial Automation Power Supply): fixed output DC 24 V (adjustable 19.2–28.8 V); rated current 27 A (peak 31 A), maximum 648 W. How long the peak can be sustained is not stated on the product page, so please inquire.
Switching DC Power Supply: output DC 12 V / 33 A, fixed single output, 400 W continuous.
Plug-In DC Power Supply: output DC 12 V / 1.2 A (14.4 W), fixed voltage, not adjustable; output plug center positive, outer negative.
Power Converter: AC 220 V input, DC 24 V / 40 mA (about 1 W) output; the product page says it is only for LED indicator lamps and low-power loads, and that to drive a PLC or relay coils (usually 100 mA or more), you should choose a higher-power power module.
Power Module: output DC 5 V / 8.5 A; the product page says it is a power module dedicated to the base unit of one PLC series, not a general-purpose 24 V supply.
Power Conversion Module: the input is DC 18–30 V, not AC; outputs 5 V (up to 35 A) and 2.1 V; the product page says it is used in the subrack of a particular control system. It is outside this article’s “AC to DC” scope; it is listed here because the output specifications of the power-related product pages on the site differ greatly, and specifications should be checked before ordering.
Stage ②: Power Margin and Temperature — How Much It Can Still Deliver When the Cabinet Is Hot
How to do it:
Leave margin first: after adding up all the load current, add about another 25% so there is room for equipment added later (this article’s own synthesis). Example: if the 24 V equipment totals 6 A, multiplying by 1.25 gives 7.5 A, so choose a specification rated at no less than 7.5 A; if there is no 7.5 A model, go up to the next size.
Then look at derating: at higher temperatures, the current or power a power supply can deliver falls. Compare on the basis of “how much it can still deliver under high-temperature conditions inside the cabinet,” not the rated value on the nameplate.
The derating curve is in the datasheet: the horizontal axis is ambient temperature and the vertical axis is the usable load. The datasheet also gives derating for different input voltages, with or without a fan, mounting orientation, and altitude.
Rated load
What it can actually deliver when the cabinet is hot
Derating zone: the hotter it is, the less it can deliver
Derating starting point
Cabinet high temperature
Upper temperature limit
Ambient temperature (inside cabinet) →
Usable load →
Figure 2 What a derating curve looks like (schematic, not to scale; the actual derating starting point, slope, and upper limit follow each model’s datasheet)
What public sources say: An electronic components maker’s blog (2019) gives examples: one natural-convection power supply can run at full load up to 50 °C ambient, must be reduced to below 80% of rating at 60 °C, and 70 °C is the upper limit beyond which it should not be used at any load; another 300 W AC-to-DC power supply, under natural convection, delivers at most 200 W at 90 to 200 Vac input and at most 250 W at 220 to 264 Vac input, and reaches 300 W only with a 10 CFM fan — showing that both input voltage and fans change the derating. A power supply distributor’s public guide says to choose by the derated current at “the cabinet ambient temperature in extreme conditions,” not the nameplate current, and recommends leaving 25% margin; the sponsored article in electronics media says many industrial power supplies must be derated as temperature rises, and recommends reserving 20% to 30% for growth. An automation maker’s specification document (24 V, 10 A model) says: 10 A continuous output, plus a short-time peak of 15 A for typically about 4 seconds; between 60 and 70 °C, derate by 6 W for each 1 °C increase; above 2,000 meters altitude, derate a further 15 W per 1,000 meters (or lower the maximum ambient temperature by 5 °C); operating temperature minus 25 to 70 °C (Notes Tables 1 and 2).
How Jiahon can help:
DC Power Supply (Ultra-Wide Input Industrial Automation Power Supply): the product page says operating temperature −10 to +50 °C, “derated operation up to +70 °C”; the derating curve (at what temperature derating starts and by how much) and whether it has a fan are not stated on the product page, so please inquire.
DC Power Supply: the product page says fanless, natural convection, operating temperature −25 to +60 °C; the derating curve and differences at different input voltages are not stated on the product page, so please inquire.
Switching DC Power Supply: the product page says active cooling with a built-in 40 mm fan; operating temperature range and derating are not stated on the product page, so please inquire.
Plug-In DC Power Supply: operating temperature 0 to +40 °C; derating is not stated, so please inquire.
Power Converter: operating temperature −10 to +55 °C; derating is not stated, so please inquire.
Power Module, Power Conversion Module: operating temperature and derating are not stated on the product pages, so please inquire.
Stage ③: Input and Form Factor — It Connects and It Fits
How to do it:
First confirm the supply: voltage (110 V or 220 V), single-phase or three-phase, and frequency. Then check whether the power supply’s input range covers it; wide-range input models work across sites with different voltages (this article’s own synthesis).
Look at inrush current at power-on and power factor: when several units power on at the same time, inrush currents add up, so the upstream overcurrent protective device should be of a type that can withstand it (this article’s own synthesis).
There are four form factors: DIN rail (mounted on the cabinet’s rail), enclosed (screwed into a machine or equipment), rack-mount (installed in a rack, for example 1U), and plug-in (small loads, plugged into an outlet). DIN rail is convenient in a cabinet; for units placed inside equipment, look at the mounting holes and cooling space (this article’s own synthesis).
Mounting orientation also affects derating: if it is not installed in the orientation given in the datasheet, the usable current falls further.
What public sources say: An automation maker’s specification document (24 V, 10 A model, single-phase) says: nominal input 100 to 240 V (±15%), continuous operation at 85 to 276 Vac; power factor about 0.99 (100 V), 0.98 (120 V), 0.92 (230 V); typical inrush current peak about 5 A (100 V), 4 A (120 V), 7 A (230 V), maximum 10 A peak; hold-up time on input interruption about 26 to 28 milliseconds; installation in a non-standard orientation requires additional derating. The sponsored article in electronics media says DIN rail types are used in control cabinets, and enclosed types inside machines and by equipment makers; a power supply distributor’s public guide says DIN rail types mount on 35 mm rail (Notes Tables 2 and 3).
How Jiahon can help:
DC Power Supply: input AC 100–240 V; DIN rail mounting; about 125×40×118 mm, 800 g. Inrush current and power factor are not stated on the product page, so please inquire.
DC Power Supply (Ultra-Wide Input Industrial Automation Power Supply): input AC 85–265 V (47–63 Hz) or DC 120–330 V; about 100×82×165 mm, 1.6 kg. Whether the form factor is DIN rail or enclosed, the mounting orientation, inrush current, and power factor are not stated on the product page, so please inquire.
Switching DC Power Supply: input AC 90–264 V (47–63 Hz); 1U rack-mount, about 190×100×40.5 mm, 1.3 kg; the input connector is C14 (a standard computer power cord). Inrush current and power factor are not stated on the product page, so please inquire.
Plug-In DC Power Supply: input AC 100–240 V; Taiwan two-pin parallel flat plug, ungrounded; about 82×43×28 mm.
Power Converter: input AC 220 V only (198–242 V), cannot be connected to 110 V; DIN rail or screw mounting; about 40×62×57.5 mm, 80 g.
Power Module: input AC 100–240 V (−15% to +10%); maximum input 160 VA; the product page says surge current 20 A (within 8 ms), hold-up time 20 ms or more (70% load); mounts on a dedicated base, M3.5 screw terminals.
Power Conversion Module: input DC 18–30 V; plug-in mounting in a subrack, about 243×117×54 mm, 1.6 kg.
Stage ④: Protection, Redundancy, and Certification — What Happens When It Fails
How to do it:
Protection: the specification table should have at least four items: short circuit, overcurrent, overvoltage, and overtemperature (the public guide says these four should be standard); then check whether, after these protections trip, it recovers automatically or needs to be power-cycled.
Status signal: with a “DC OK” relay contact or indicator lamp, the control cabinet can tell which power supply has failed.
Redundancy: for important loads, use two units in parallel (1+1) with a isolation module in between; units in parallel should be from the same series, with output voltages adjusted close to each other; add a separate fuse to each unit’s input. The purpose of the isolation module is to separate the two units’ outputs so that if one fails, it does not affect the other (this article’s own synthesis).
Certification: check against the safety standards your equipment or customer requires, and confirm that the model has the corresponding certificates; where power is supplied to external devices and installation is done by third parties, consider models marked “Limited Power Source” (LPS) (this article’s own synthesis).
What public sources say: A power supply distributor’s public guide says short-circuit, overcurrent, overvoltage, and overtemperature protection should be standard; a DC OK relay contact or LED lets the control panel report a power supply fault; the approvals listed for industrial use are EN/IEC 62368-1 and EN 61204-3. A power supply maker’s public page summarizes the safety standards for industrial automation power supplies: EN/IEC 62368-1 is a hazard-based standard that replaces the older EN 60950-1, EN 60065, and others; EN/IEC 61010-2-201 covers control equipment for measurement, control, and laboratory equipment; the output of a Limited Power Source (LPS) is usually below 30 V (DC or AC rms), with short-circuit current not exceeding 8 A and power not exceeding 100 W; it also lists protection classes I (requires grounding), II (double insulation), III (safety extra-low voltage), and IP ratings. Another power supply maker’s blog (2012) explains that the purpose of LPS is so that third-party installers do not have to anticipate every kind of fault that could occur inside the power supply; for models with output above 30 V up to 60 V, the current limit is 150 divided by the output voltage, and power does not exceed 100 W. An automation maker’s specification document says: the DC OK contact opens when the output falls 10% or more below the set value; units in parallel should be the same series, with output voltage difference within about ±500 mV; the simple form of redundancy is 1+1, and it recommends adding a isolation module and a separate fuse on each unit’s input (Notes Table 4).
How Jiahon can help:
DC Power Supply: the product page says triple protection against overcurrent, overvoltage, and overtemperature, with automatic reset after a fault. Short-circuit protection, a DC OK signal, whether it can be paralleled, and safety certificates are not stated on the product page, so please inquire.
Plug-In DC Power Supply: the product page says overvoltage, overcurrent, short-circuit, and overtemperature protection with automatic recovery; it also says efficiency meets ENERGY STAR Level VI. Safety certificates are not stated on the product page, so please inquire.
Switching DC Power Supply: the product page says the ventilation hole design conforms to IEC 62368, and the efficiency is 80 PLUS Bronze grade (an efficiency certification, not a safety certification). Protection items, a DC OK signal, whether it can be paralleled, and safety certificates are not stated on the product page, so please inquire.
Power Module: the product page says overcurrent protection cuts off automatically at 9.9 A or more; other protection and certification are not stated on the product page, so please inquire.
Power Conversion Module: the product page says it supports multiple units in parallel (n+1 redundancy), is hot-swappable, can connect two 24 V supplies, and has a built-in monitoring signal (the signal terminal is grounded when normal, and open on fault or absence). This model has DC 18–30 V input and is used in the subrack of a particular control system; it is not a general-purpose AC-to-DC power supply. For how to set up parallel redundancy in a general control cabinet, please inquire.
DC Power Supply (Ultra-Wide Input Industrial Automation Power Supply): protection items, a DC OK signal, whether it can be paralleled, and safety certificates are not stated on the product page, so please inquire.
Redundancy modules, rails, and fuses for power supplies: if you need them, please inquire.
Further reading
To look at the related process steps together, you can go on to read:
- “How Tightly to Control Plant Temperature and Humidity: Which Conditions Matter for Solder Paste, Moisture-Sensitive Parts, and ESD — 5 Stages from Setting Windows to Audits“: how to measure and manage the ambient temperature of cabinets and the plant
When you need to match types, please prepare four items first: the voltage and current of each piece of equipment, the upper temperature limit of the site cabinet, the supply voltage and phases, and whether redundancy is needed and which safety standards must be met. You are welcome to contact Jiahon.
Further reading: “Power Supply vs. UPS: What’s the Difference“
Notes: Sources and Exceptions
The following is for those who need to verify; skipping it does not affect the method above. Where your process specifications, the power supply’s written specifications, or safety standards differ from this article, they take precedence.
Sources for each stage
| Source | Which stages and content it is used for | From |
|---|---|---|
| Source 1 | Stages ① to ④: current at 100 W, fine adjustment, power-on peaks, margin, derating principle, rail width, protection items, DC OK, approval list | A power supply distributor’s public guide (the page states no year; the footer copyright says 2026) |
| Source 2 | Stages ① to ③: common output voltages, summing power consumption and margin, environmental factors, form factor categories | A sponsored article by an electronic components distributor published in electronics media (July 28, 2026; marketing in nature) |
| Source 3 | Stages ② to ④: derating, input range, inrush current, hold-up time, DC OK, and parallel redundancy for a 24 V, 10 A model | An automation maker’s specification document (document version 00, no year stated) |
| Source 4 | Stage ②: examples of derating curves | An electronic components maker’s blog (November 5, 2019) |
| Source 5 | Stage ④: safety standards, Limited Power Source, protection classes | A power supply maker’s public page (no year stated) |
| Source 6 | Stage ④: the purpose and limits of Limited Power Source | Another power supply maker’s blog (June 13, 2012) |
| Jiahon material | “How Jiahon can help” | Jiahon product pages and articles |
Table 1 | Load, margin, and derating
| Item | Content | Source |
|---|---|---|
| Current at 100 W | 12 V about 8.3 A; 24 V about 4.2 A; 12 V needs thicker wire and has greater voltage drop | Source 1 |
| Common output voltages | 24 V is common; also 5 V, 12 V, 15 V, 48 V, and multiple outputs | Source 2 |
| Output fine adjustment | About ±10% on most good-quality power supplies | Source 1 |
| Power-on peaks | Contactors, solenoid valves, and capacitive loads draw many times steady-state current; choose a model with a clearly stated peak power range | Source 1 |
| Margin | About 25% (Source 1); 20% to 30% (Source 2) | Sources 1, 2 |
| Derating principle | Choose by the derated current at the cabinet temperature in extreme conditions, not the nameplate current | Source 1 |
| Environmental factors | Ambient temperature, cabinet ventilation, mounting orientation, altitude, humidity, protection rating, vibration | Source 2 |
Table 2 | Examples of derating and specification documents
| Item | Content | Source |
|---|---|---|
| A natural-convection power supply | Full load at 50 °C and below; reduced to below 80% of rating at 60 °C; 70 °C is the upper limit | Source 4 |
| A 300 W power supply | AC to DC; natural convection: at most 200 W at 90 to 200 Vac input, at most 250 W at 220 to 264 Vac; up to 300 W with a 10 CFM fan | Source 4 |
| Derating of the 24 V, 10 A model | 10 A continuous output; short-time peak 15 A, typically about 4 seconds; between 60 and 70 °C, derate 6 W per 1 °C rise; above 2,000 meters altitude, derate 15 W per 1,000 meters (or lower the maximum ambient temperature by 5 °C); additional derating for non-standard mounting orientation | Source 3 |
| Temperature of the 24 V, 10 A model | Operating temperature minus 25 °C to 70 °C | Source 3 |
Table 3 | Input, inrush current, and form factor
| Item | Content | Source |
|---|---|---|
| Input range (24 V, 10 A model) | Nominal 100 to 240 V (±15%), continuous operation 85 to 276 Vac; single-phase | Source 3 |
| Power factor (typical) | 0.99 at 100 V; 0.98 at 120 V; 0.92 at 230 V | Source 3 |
| Inrush current (typical peak) | 5 A at 100 V; 4 A at 120 V; 7 A at 230 V; maximum 10 A peak | Source 3 |
| Hold-up time | About 26 to 28 milliseconds after input interruption (10 A, 24 V) | Source 3 |
| Efficiency (typical) | About 91.2% to 93.0% | Source 3 |
| Form factor | DIN rail types for control cabinets; enclosed types for machines and equipment makers; rail is 35 mm | Sources 2, 1 |
Table 4 | Protection, redundancy, and safety standards
| Item | Content | Source |
|---|---|---|
| Protection | Short circuit, overcurrent, overvoltage, and overtemperature should be standard; DC OK contact or indicator lamp | Sources 1, 2 |
| Approvals (industrial) | EN/IEC 62368-1, EN 61204-3 | Source 1 |
| EN/IEC 62368-1 | Hazard-based; replaces EN 60950-1, EN 60065, and other older standards | Source 5 |
| EN/IEC 61010-2-201 | Control equipment for measurement, control, and laboratory equipment | Source 5 |
| Limited Power Source (LPS) | Output usually below 30 V; short-circuit current not exceeding 8 A, power not exceeding 100 W; above 30 V up to 60 V, current not exceeding 150 divided by the output voltage, power not exceeding 100 W | Sources 5, 6 |
| Purpose of LPS | Third-party installers do not have to anticipate every fault; makers verify by methods such as load limits and simulating internal faults | Source 6 |
| Protection classes | I requires grounding; II is double insulation; III is safety extra-low voltage; IP is the dust and water protection rating | Source 5 |
| DC OK contact (10 A model) | 24 V, 10 A model: opens when the output falls 10% or more below the set value | Source 3 |
| Parallel and redundancy (10 A model) | 24 V, 10 A model: same series; output voltage difference within about ±500 mV; 1+1 is simple; a isolation module and a fuse on each unit’s input are recommended | Source 3 |
Standards cited
For the standards cited in this article, please refer to the current edition from each issuing body.
IEC 62368-1 “Audio/video, information and communication technology equipment — Part 1: Safety requirements”
Issuing body: IEC (International Electrotechnical Commission)IEC 61010-2-201 “Safety requirements for electrical equipment for measurement, control and laboratory use — Part 2-201: Particular requirements for control equipment”
Issuing body: IEC (International Electrotechnical Commission)IEC 61204-3 “Low-voltage power supplies, d.c. output — Part 3: Electromagnetic compatibility (EMC)”
Issuing body: IEC (International Electrotechnical Commission)
This is the general case; individual situations still need to be assessed case by case.
Exceptions and limits
What was and was not seen: This article draws on a power supply distributor’s public guide (the page states no year), a sponsored article by an electronic components distributor published in electronics media (July 28, 2026), an automation maker’s specification document (24 V, 10 A model, version 00, no year stated), an electronic components maker’s 2019 blog, a power supply maker’s page summarizing safety standards (no year stated), and another power supply maker’s 2012 blog. The full texts of IEC/EN 62368-1, 61010-2-201, and 61204-3 were not read; the content and figures of the standards are taken from how the public pages above relay them; the English titles of the standards are taken from the standards body’s catalog pages, and Source 1 lists only the number for EN 61204-3.
Sources with a stake: Source 1 is a power supply distributor’s promotional page; Source 2 is a distributor’s sponsored article, from which only general advice is taken; Sources 5 and 6 are power supply makers’ pages.
Figures from “one model”: the figures in the specification document and on derating are all examples from one model, not selection thresholds; they differ between makers and series.
Inconsistencies within source pages: Source 5 writes the number for 62368-1 inconsistently, writes the older standards it replaces as “and others” (the list may not be complete), and says only “usually” for the 30 V of Limited Power Source; Source 6’s page keywords say 60950-1, while the text discusses 62368-1. This article follows the standards’ own numbers.
Dates: Sources 1 and 5 state no year; Source 2 is 2026; Source 4 is 2019; Source 6 is 2012, and its content may not reflect the current edition.
This article’s own synthesis: the following are this article’s synthesis from the sources, not written this way in the sources: in Stage ①, “for long cable runs, give priority to the higher voltage”; in Stage ②, “about 25% margin” is taken from Source 1’s recommendation, and “6 A times 1.25 is 7.5 A, go up to the next size” is this article’s worked example; in Stage ③, “wide-range input works across different voltages,” “when several units power on at the same time, inrush currents add up, and the upstream overcurrent protective device should be one that can withstand it,” “DIN rail is convenient; inside equipment, look at mounting holes and cooling,” and “rack-mount” (taken from the 1U model on a product page); in Stage ④, “the purpose of the isolation module” and “consider models marked LPS.” The sources gave only the values for input range and inrush current.
Scope: This article covers only AC-to-DC power supplies; it does not cover DC-to-DC converters (the power conversion module listed in Stages ① and ④ only illustrates the differences among products on the site), three-phase input, installation and wiring, prices, or lead times.
Equipment and products: The figures and statements in “How Jiahon can help” are text read from the product pages on October 13, 2026; product images and specification sheets were not reviewed, and they were not verified by this article; specifications follow the product pages, and for anything not stated there, please inquire. The product pages’ “also featured” sections and buying suggestions are the product pages’ own marketing language and are not cited in this article.
This article is a summary of the general case. It is not a restatement of standard clauses, not an endorsement of any maker, equipment manufacturer, or service provider, and still less a promise about your equipment and processes. Please rely on your equipment specifications, the power supply’s written specifications and safety standards, and your own verification; this is the general case, and individual situations still need to be assessed case by case.