You’re concerned your computer troubles stem from a failing (or outright fried) power supply unit. How can you test the unit to be sure that it’s the source of your hardware headaches?

Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.

The Question

SuperUser reader Sam Hoice has some PSU concerns:

My computer powered off the other day on its own, and now when I push the power button, nothing happens. My assumption would naturally be that the power supply is done (possibly well done) but is there any good way to test this before I buy a new one?

How can Sam test things without damaging his current computer or other hardware?

The Answer

SuperUser contributor Grant writes:

Unplug the power supply from any of the components inside the computer (or just remove it from the computer completely).

USE CAUTION HERE (Though you’d only be shocked with a max of 24 volts)

1. Plug the power supply into the wall.
2. Find the big 24-ish pin connector that connects to the motherboard.
3. Connect the GREEN wire with the adjacent BLACK wire.
4. The power supply’s fan should start up. If it doesn’t then it’s dead.
5. If the fan starts up, then it could be the motherboard that’s dead. You can use a multimeter to check if there is power output from the power supply.

Adrien offers a solution for readers who may not be comfortable jamming wires into their power supply unit’s MOBO connector:

Most well-stocked geek-stores sell a “power-supply tester” that has all the appropriate connectors to plug each part of your PSU into, with spiffy LEDs indicating status of the various rails, connectors for IDE/SATA/floppy power cables, etc. They run ~$20 US.

With a little careful shopping you can even find a highly-rated PSU tester for a measly $6.

Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.