How to Use a Power Supply Tester to Test a PSU

If you are comfortable working on PCs, you can test the power supply

Photo of an Innoo Tech Power Supply Tester
Innoo Tech Power Supply Tester. © Innoo Tech

Testing a power supply on a desktop computer using a power supply tester device is one of two ways to test a power supply in a computer. There should be little doubt about whether your PSU is working properly after testing it with a power supply tester.

This process is not for a beginner. However, if you are comfortable working on your computer, testing a power supply with a power supply tester device usually takes around 30 minutes.

Before you begin, read Important PC Repair Safety Tips. Testing a power supply unit involves working around high voltage electricity, which is a potentially dangerous activity. Do not skip this step. Safety should be your primary concern during a power supply test with a PSU tester.

These instructions apply specifically to the Coolmax PS-228 ATX Power Supply Tester, but they also suffice for most other power supply testers with an LCD.

How to Test a Power Supply Using a Power Supply Tester

After you read the safety tips, it's time to get started:

  1. Turn off the PC, remove the power cable, and unplug anything else connected to the outside of the computer. Then, open the case. To make the power supply test easier, move the disconnected and open case somewhere you can easily work with it such as to a table or other flat, nonstatic surface.

  2. Unplug the power connectors from every internal device inside the computer. An easy way to make sure each power connector is unplugged is to work from the power cable bundle coming from the power supply. Each group of wires should terminate at one or more power connectors. It's not necessary to remove the actual power supply from the computer, nor should you need to disconnect any data cables or other cables not connected to the power supply.

  3. Group all the power cables and connectors together for easy testing. As you organizing the power cables, pull them away from the computer case as much as possible to make it easy to plug the power connectors into the power supply tester.

  4. Check to make sure that the power supply voltage switch located on the power supply is properly set for your country. In the U.S., this switch should be set to 110V/115V.

  5. Plug both the ATX 24 pin Motherboard Power Connector and ATX 4 pin Motherboard Power Connector into the power supply tester. Depending on the power supply that you have, you may not have a 4 pin motherboard connector but instead have a 6 pin or 8 pin variety. If you have more than one type, only plug in one at a time along with the 24 pin main power connector.

  6. Plug the power supply into a live outlet and flip the switch on the back. Some power supplies do not have a switch on the back. If the PSU you're testing does not, plugging in the device is sufficient to provide power.

  7. Press and hold the ON/OFF button on the power supply tester. You should hear the fan inside the power supply begin to run. Some versions of the Coolmax PS-228 power supply tester do not require that you hold down the power button, but others do. Just because the fan is running does not mean that your power supply is supplying power to your devices properly. Also, some power supply fans do not run when being tested with a power supply tester even though the PSU is fine. You need to continue testing to confirm anything.

  8. Confirm the LCD on the power supply tester is lit, and you see numbers in all the fields. The motherboard power connectors plugged into the power supply tester support the entire range of voltages that your PSU can deliver, including +3.3 VDC, +5 VDC, +12 VDC, and -12 VDC. If any voltage reads "LL" or "HH" or if the LCD screen does not light up at all, the power supply is not working properly. You need to replace it. You're just looking at the LCD screen at this point. Don't worry about any other lights or voltage indicators not located on the actual LCD readout.

  9. Check Power Supply Voltage Tolerances and confirm that the voltages reported by the power supply tester are within approved limits. If any voltage is outside of the range shown, or the PG Delay value isn't between 100 and 500 ms, replace the power supply. The power supply tester is designed to give an error when a voltage is out of range, but you should check yourself to be safe. If all the reported voltages fall within tolerance, you've confirmed that your power supply is working properly. If you'd like to test the individual peripheral power connectors, continue testing. If not, skip to Step 15.

  10. Turn off the switch on the back of the power supply and unplug it from the wall.

  11. Plug in one connector to the appropriate slot on the power supply tester: a 15 pin SATA Power Connector or a 4 pin Molex Power Connector. Do not connect more than one of these peripheral power connectors at a time. You probably won't damage the power supply tester doing so, but you won't be accurately testing the power connectors either. Both of the motherboard power connectors that you connected to the power supply tester in Step 6 should remain plugged in throughout these tests of the other power connectors.

  12. Plug in the power supply and then flip on the switch on the back if you have one.

  13. The lights labeled +12V, +3.3V, and +5V correspond to the voltages being delivered through the connected peripheral power connector and should light up appropriately. If not, replace the power supply. Only the SATA power connector delivers +3.3 VDC. You can see the voltages delivered by the different power connectors by looking at the ATX Power Supply Pinout Tables. Repeat this process, beginning with Step 11, testing the voltages for the other power connectors. Only test one at a time, not counting the motherboard power connectors that stay connected to the power supply tester the entire time.

  14. When the testing is complete, turn off and unplug the power supply, disconnect the power cables from the power supply tester, and then reconnect the internal devices to power. Assuming your power supply tested good or you've replaced it with a new one, you can now turn your computer back on and/or continue troubleshooting the problem you are having.

A power supply test using a power supply tester is not a true "load" test — a test of the power supply under more realistic usage conditions. A manual power supply test using a multimeter, while not a perfect load test, comes closer.

The Test Proves Your PSU Is Good, but Your PC Won't Start

There are several reasons a computer won't start other than a malfunctioning power supply.

See How To Troubleshoot a Computer That Won't Turn On for a troubleshooting guide and more help with this problem.