How to Use a Power Supply Tester to Test a PSU

Tim Fisher has more than 30 years' of professional technology experience. He's been writing about tech for more than two decades and serves as the SVP and General Manager of Lifewire.

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What to Know

• Read PC Repair Safety Tips. Open case, unplug and organize power connectors. Check for proper voltage.
• Next, plug motherboard power connectors into power supply tester. Plug power supply into live outlet.
• Press and hold ON/OFF button on tester. Check power supply voltage tolerances and other criteria.

This article explains how to test the power supply unit (PSU) in your computer with a power supply tester. Instructions apply specifically to the Coolmax PS-228 ATX power supply tester, but they also suffice for most other PSU testers with an LCD.

Read Important Computer Repair Safety Tips before proceeding with testing a power supply unit. Working with high voltage electricity can be dangerous, and it's crucial to prioritize safety when repairing a power supply. Do not neglect this step.

How to Test the Power Supply in a Computer

How to Test a Power Supply Using a Power Supply Tester

If you have some experience working on your computer and feel comfortable following instructions, this process should take about 30 minutes to complete. However, it may not be suitable for those who are new to computer maintenance. Before proceeding, be sure to read the safety tips. Once you have done so, you can begin the process.

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, non-static surface.

Just because the fan is running doesn't mean your power supply is supplying power to your devices properly. Also, some power supply fans don't run when being tested even though the PSU is fine. You need to continue testing to confirm anything.

A test using a power supply tester isn't 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.

Your PSU Is Good, But Your PC Won't Start

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

However, there are several reasons a computer won't start other than a malfunctioning power supply. See How to Fix a Computer That Won't Turn On for a troubleshooting guide and more help with this problem.

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