Before You Start: Safety

Working with PSUs carries electrical risk. Always: unplug the PSU from the wall before making any connections. Never open the PSU casing — capacitors inside can hold dangerous charges. Work on a non-conductive surface. Do not short-circuit the PSU to live mains power.

Method 1: Paperclip Test (Power-On Check)

  1. 1

    Disconnect the PSU from all components

    Unplug the PC and disconnect all power connectors from the motherboard, drives and graphics card. You want the PSU isolated from all components for this test.

  2. 2

    Locate the green wire on the 24-pin connector

    The large 24-pin ATX connector has one green wire (PS_ON signal, pin 16). All other wires are black (ground), yellow (12V), red (5V) or orange (3.3V). The green wire is the power-on signal — when shorted to ground, the PSU starts.

  3. 3

    Short green to black with a paperclip

    Bend a paperclip into a U shape. Insert one end into the green wire pin and the other into an adjacent black wire pin on the 24-pin connector. Plug the PSU back in and flip the rear switch on. The PSU fan should spin — confirming the PSU is powering on. This does not test voltages, only that the PSU activates.

Method 2: Multimeter Voltage Test

  1. 4

    Test Molex connector voltages under load

    With the PSU powered on (paperclip in 24-pin), connect a Molex connector from the PSU. Set your multimeter to DC Voltage. Test: yellow wire (12V rail) to black ground — should read 11.4–12.6V. Red wire (5V rail) to black ground — should read 4.75–5.25V. Significant deviation from these ranges indicates a failing PSU.

Method 3: PSU Tester (Easiest)

A dedicated PSU tester ($15–30 from Jaycar, Scorptec, or online) connects to all PSU connectors and displays all rail voltages simultaneously with a pass/fail indication. Far easier than a multimeter for a comprehensive test. Worth buying if you build or service PCs regularly.

Frequently Asked Questions

Random shutdowns or restarts under load (when running games or demanding applications), failure to boot or intermittent boot failures, blue screens of death (BSOD) that resolve when the system is cooler, burning smell from the PC case, unusually loud fan noise from the PSU, or the PC simply not turning on at all. PSU failures often present as symptoms that look like other hardware problems — testing the PSU is a worthwhile early step in PC troubleshooting.
Quality PSUs from reputable brands (Corsair, Seasonic, EVGA, be quiet!) typically last 5–10 years. Budget PSUs may fail sooner, particularly under sustained heavy loads. The PSU is the one component where buying quality pays off — a failing PSU can damage other components when it fails. Most quality PSUs carry 3–10 year warranties.