Last weekend a friend of mine brought his computer to me. He was at the end of his rope with his machine and why it wouldn't complete POST. He had replaced the memory, he had replaced the CPU, and was getting ready to order a motherboard, since his was out of warranty.

He would not have done ANY of this, if he had talked to me first. When he brought his machine over, I had asked what he had done, and my first reaction was to say, "sounds like a dead power supply". His response is one that I see a lot in this sub, and it drives me CRAZY:

"It can't be the power supply - I did the paperclip test and it starts up! I know the power supply works!"

After I picked myself up from the mild stroke I had, I went out to my garage, grabbed my tech kit, and grabbed one of my favorite tools: my power supply tester. 10 seconds later, I confirmed what I basically already knew: the 5V rail and the CPU's 12V rail was dead. This despite the power supply running.

A power supply tester is only about $15, folks. It's a tool that, IMO everyone who gets inside their machine should have, even if they don't have a problem. It's like a plunger - better to have BEFORE you need one. If for no other reason than you can check yours or loan it to friends.

The paperclip test means JACK as far as knowing your power supply is functioning. Literally all it proves is that the power supply will startup. But that's like saying a car that is up on blocks can drive to the store because the engine starts up.

Edit: because a lot of folks have brought them up, I'll go ahead and address multimeters. They are absolutely a good substitute if you don't have a power supply tester similar to the one I linked. My only complaint with them is that, I don't know about everyone else here, but I don't have the pin-out diagram of power supply connectors memorized (hell - I still have to lookup a patch cable diagram when I make a CAT6 cable as I have it largely memorized but I want to be 100% certain). So I'd have to follow a diagram and ensure that I'm connecting the proper connector pins in sequence and verify that they are putting out the correct voltages. Then consider that a modern power supply can have upwards of 50 pins or more to test (24-pin ATX, 4-8-pin CPU1, 4-8-pin CPU2, 6/8-pin PCIE1, 6/8-pin PCIE2, etc). I still recommend a tester over a multimeter simply for the sake of speed. If you have the time and patience, however, to do a multimeter test, then you're actually probably better off as this tool definitely would fall under Alton Brown's unitasker rule.