Testing a power supply safely depends on what kind it is (PC PSU, bench supply, charger, etc.), but the basic idea is to power it on, then measure its output under at least a small load. The steps below assume a common ATX PC power supply; if you mean something else, say what device it’s from.
Safety first
- Unplug the supply and wait a minute before touching any connectors; never open the PSU case because capacitors inside can hold dangerous voltage.
- Work on a non‑conductive surface, avoid loose metal objects, and if anything smells burnt or you see swelling or scorching, stop and replace the unit.
Simple “paperclip” power‑on test
- Disconnect the PSU from the motherboard and all components, leaving only the wall cord connected.
- On the 24‑pin ATX plug, short the green “PS_ON” wire to any black ground wire with a bent paperclip or jumper, then switch the PSU on; if the fan starts, the PSU can at least turn on, though this does not prove it is good under load.
Multimeter voltage test
- Leave the green‑to‑black jumper in place so the PSU stays on, then set a digital multimeter to DC volts and put the black probe on any ground (black wire).
- Measure: yellow wires should be near 12 V, red near 5 V, orange near 3.3 V; if any rail is off by more than about ±5%, the PSU is suspect and should be replaced.
Using a PSU tester
- Plug the 24‑pin ATX connector (and CPU/PCIe leads if required) into a dedicated PSU tester, then turn on the PSU.
- Read the displayed voltages and status LEDs; values outside the allowed range or error indicators mean the PSU is faulty.
When to replace instead of test more
- Replace the PSU if it fails to start, voltages are out of range, it trips off under load, or the system shows random shut‑downs or reboots that disappear with a different PSU.
- If you are unsure working around live mains or exposed connectors, using a pre‑built PSU tester or having a technician check it is the safest option.