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How to Test a Power Supply?
Updated Phones, Computers & Devices
Safety first: unplug the PSU and let it sit before handling. Never open the PSU casing itself — capacitors inside can hold a dangerous charge even when unplugged.
Signs of a failing PSU without opening the PC: random shutdowns or reboots under load, a burning smell, the fan not spinning at all, unusual buzzing or clicking, or the PC not powering on at all despite the wall outlet and cable being fine. Any of these is a reason to test rather than assume.
Method 1 — The paperclip (jump-start) test
This checks if the PSU powers on at all.
- Unplug the PSU and disconnect it from all components.
- Find the 24-pin motherboard connector. Locate the green wire (PS_ON) and any black wire (ground).
- Bend a paperclip into a U and insert one end into the green pin and the other into an adjacent black pin.
- Plug the PSU in and flip its switch. If the fan spins, the PSU is at least turning on. (No fan = likely dead PSU.)
Method 2 — Use a PSU tester
A cheap PSU tester plugs into the 24-pin (and other) connectors and displays voltages on a screen — the easiest reliable option, and the best choice if you want to check PSU health without opening the PC at all, since it just plugs into the existing connectors. Green/normal readings mean the rails are working.
Method 3 — Use a multimeter (most accurate)
- Do the paperclip jump-start so the PSU is on.
- Set your multimeter to DC voltage.
- Probe the connector pins against ground and check the rails read close to their targets below.
Rail voltages and tolerance (ATX standard)
| Rail | Target voltage | Acceptable range (±5%) |
|---|---|---|
| +12V | 12.0V | 11.4V – 12.6V |
| +5V | 5.0V | 4.75V – 5.25V |
| +3.3V | 3.3V | 3.14V – 3.47V |
| +5VSB (standby) | 5.0V | 4.75V – 5.25V |
| −12V | −12.0V | −11.4V to −12.6V |
Interpreting results: a fan that spins but wrong/unstable voltages means a failing PSU. If the fan doesn't spin at all during the jump-start, the PSU is almost certainly dead and should be replaced. Readings that drift outside tolerance under load (rather than at idle) suggest a PSU that's degrading rather than fully dead — worth replacing before it takes other components with it.
Sizing matters too, not just testing: a PSU that's simply undersized for your components can cause the same symptoms as a failing one (random shutdowns, instability under load) even when every rail tests within tolerance — if your system was recently upgraded with a more power-hungry GPU or CPU, check the PSU's rated wattage against your build's total draw before assuming it's failing.
A limitation worth knowing: both the paperclip test and a basic PSU tester check the PSU at idle, with no real load attached — a unit can pass both tests and still fail once your components draw real power under gaming or heavy workloads. If symptoms only appear under load, that's a stronger sign of a failing or undersized PSU than any of the three tests alone.
Two similar answers: How to Turn Off an Android Phone? and How to Turn Off Read Receipts?.
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