Few things are as annoying and potentially dangerous as a faulty PC power supply. The mere suspicion of an issue changes everything... and many users want to know how to test an ATX power supply. In general, we must explore three phases: basic voltage reading in the computer, voltage reading with external equipment, and finally, load tests on the power supply.
Time and space
Unfortunately, these are two non-negotiable things. Testing an ATX power supply requires time and space. If we think about it for a moment, removing the PSU from the case can become a nightmare due to cable management and other details (there are many beautiful cases on the market, but working on them is a headache).
So... if time and space are scarce, my recommendation is to replace the power supply directly. I understand that many users out there want to avoid that, but sometimes the most practical thing is to solve the problem with brute force and move on. Now, if you still want to test your ATX power supply and check if there's any issue with it, keep reading.
Voltages, voltages, voltages...
The three main voltages in an ATX power supply are 12v, 5v, and 3.3v. To confirm if they are at adequate levels without having to remove the PSU from the system, you have two options: Enter the BIOS/UEFI, or use a maintenance program. Inside the BIOS/UEFI, what you're looking for is a section called H/W Monitor, PC Health or similar. And on the software side, there are very good free options like HWiNFO (which appears in the image) or HWMonitor.
Obviously, the apparent stability of the voltages is not enough to think that everything is fine with the PSU. In fact, these readings have limitations, and some motherboards can be quite inaccurate. Personally, I usually start with a maintenance program, followed by a visit to the BIOS/UEFI if I notice that a number is wrong. If doubts persist, there's no other option but to go deeper...
And more voltages, with external hardware
One of the most interesting tools for testing an ATX power supply is the so-called tester. Basically, what you need to do is connect the power supply cables to the device (24-pin, 6/8-pin, 4/8-pin, SATA, Molex, and floppy), turn on the PSU, and wait. If there's something strange in the readings, the tester will let you know immediately. Some models have audible alarms, while others put their warnings on a small LCD screen.
These testers cost about 12 euros on average, and if you think you're going to cross swords with power supplies more than once, it's definitely a good investment. The direct alternative is to measure voltages using a classic multimeter, but once again... the voltages don't tell the whole story. Why? Because the only way to clear doubts about the stability of an ATX PSU is to put pressure on it.
Load tests
Blue screens that appear out of nowhere and computers that shut down like magic are two very common symptoms of a failing ATX power supply, especially when we try to run a heavier task than usual. Many users discover problems with their power supplies while trying to play, but video games are not the only option.
With a good combination of Cinebench R23, Unigine Heaven, AIDA64 Extreme, Prime95, and FurMark, any user will be able to check almost definitively whether their ATX PSU is stable or not. AIDA64 Extreme's general benchmark is a good starting point, then move to CPU (Cinebench, Prime95) and GPU (Heaven, FurMark). In more extreme cases, you can combine Prime95 with FurMark and attack both components at once.
How to turn on an ATX PSU outside the PC
Unlike old AT power supplies that used a conventional switch, ATX power supplies depend on a «signal» to start, but we can easily fool them: All we need is to create a bridge between the green wire (PS_ON) and any of the ground wires before connecting the power. If all the cables of the ATX PSU are black, you can use the image or the pinout as a reference. (Editor's note: The bridge is not necessary if you use a tester, and it's only useful to work with the power supply outside the system.)
ATX PSU or temperature?
A classic problem when testing an ATX power supply is that the user can confuse their diagnosis and end up blaming the power supply, when in reality there is an excess of heat in the system. A good cleaning and a change of thermal paste on the processor are essential for the stability of the computer not to fall apart. The same happens with graphics cards, but their temperature peaks usually reflect a performance loss associated with the drop in their frequencies.
How to test an ATX power supply: If doubts persist... replace it
Personally, I like to repair everything I can, and save money if the DIY route allows it. However, the ATX PSU is an essential component. If you have some experience in electronics and think you can repair it, then I'm not going to stop you (and most likely you won't need this article)... but if after a long diagnostic session you still have doubts about its operation, don't think twice: Look for a new unit, of good quality, and with a warranty.
At the end of the day, the risk is too great. A catastrophic failure in an ATX PSU can destroy other components in an instant... and I think I don't need to explain what a graphics card is worth in this chaotic market. Look for reviews, compare specifications, and remember that the 80 Plus rating is not synonymous with quality. Good luck!
