How to Test Your Computer’s PSU With a PSU Tester
A PSU tester is one of the easiest ways to test your computer’s PSU because it offers an all-in-one experience with instant, actionable feedback.
Why use a power supply tester?
PSU testers are so cheap and so easy to use that we really can’t recommend them highly enough. If you have a multimeter it’s convenient to use and you don’t mind testing a few pins and taking notes, you can certainly test your power supply the old fashioned way.
But in addition to the simple plug-and-play operation of a power supply tester, it has a significant advantage over performing the test manually.
A PSU tester is designed specifically for this task, giving you both instant feedback on whether or not the connectors match the expected voltage and configuration, and loudly warning you when they don’t.
In addition, it allows for easy testing of the SATA connectors (there is no way to simply test the tiny pinout on a SATA connector with a multimeter) and gives you a readout for the PG value – the “Power Good” time until the start period – a multimeter cannot do that.
Finally, a word about PSU testers: They all look about the same because they’re all about the same. There are dozens of brands that look exactly like the model we recommend above since basic PSU testers are a “white box” product.
Some factories turn out a bajillion of these, and various companies pay to have their specific case and/or logo stamped onto the circuit board. But inside they are identical. Should you be reading this article and the specific PSU tester we linked above (and using for this tutorial) is out of stock, you can simply purchase another one that looks exactly like this one or this one.
How to use a power supply tester
Using a PSU tester is easy, but you should always follow best practices. How to safely test your power supply with a tester.
Warning: At no point will we open the power supply ourselves. If you do this without proper precautions, knowledge, and tools, you could be in for a fatal shock.
Disconnect the cables before testing your power supply
Turn off your power supply. If it has a switch, you can use the switch on the back. Otherwise, disconnect it. Before using the PSU Tester, we recommend unplugging not only the cable to be tested, but all cables connecting your PSU to internal components.
Not only does this protect the various components should anything go wrong, but it’s also a good idea to test each cable at once to ensure the power supply is working properly across the board.
Attach the power supply tester and turn on the power supply
The PSU Tester draws power from the PSU itself. To use it, simply turn off the PSU (either with the switch on the back or by unplugging it from the wall outlet).
Then connect the mother power cable as well as the CPU power connector cable to the tester – if you don’t connect the CPU cable you will get an error message. Turn on the power supply.
Reading the results of the PSU tester
The tester will show you different performance categories it expects from the motherboard and CPU cables like -12V, +12V, +3.3V etc. Under these categories, it will show you the actual voltage.
It’s okay if these values don’t match exactly. If the -12V reading is 11.8, that is well within the expected ±5% range that is acceptable for this connection. And if it’s out of range, the tester will warn you — no math or knowledge of the acceptable range is required.
It also shows you the PG value. This value indicates how long it took your power supply to ramp up to full voltage from the first sign of power activity on all ports.
An acceptable value is 100-500 milliseconds. A higher value can indicate faulty PSU components, and too high a PG value can cause your computer to get stuck in a boot loop because your hardware components don’t turn on in the expected window.
You can test other connections including PCI-E, MOLEX, SATA, and 4-pin floppy connectors to ensure each connection delivers the expected output.
Most testers, including this one, have a simple LED indicator light to show the voltages when testing the secondary wires. For this reason, you must test the cables individually (e.g. do not connect a SATA cable and a MOLEX drive connector at the same time).
It won’t harm the tester or the power supply, but you won’t get an accurate reading of their respective voltages since there’s only one set of LED indicators.
If your PSU tests show that the expected voltages are out of specification (e.g. you are getting 8 volts for one of the connections when 12 is expected) or your PG is over 500 milliseconds, it is time to replace your PSU.