How to Test a Power Supply?

If your PC won't power on, testing the power supply unit (PSU) helps confirm whether it's the culprit. There are three common methods, from quickest to most thorough.

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.

Method 1 — The paperclip (jump-start) test:

This checks if the PSU powers on at all.

1. Unplug the PSU and disconnect it from all components.
2. Find the 24-pin motherboard connector. Locate the green wire (PS_ON) and any black wire (ground).
3. Bend a paperclip into a U and insert one end into the green pin and the other into an adjacent black pin.
4. 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. Green/normal readings mean the rails are working.

Method 3 — Use a multimeter (most accurate):

1. Do the paperclip jump-start so the PSU is on.
2. Set your multimeter to DC voltage.
3. Probe the connector pins against ground and check the rails read close to their targets: +12V, +5V, and +3.3V (acceptable tolerance is usually within about 5%).

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.