How do I know if my PC power supply is bad?

The most obvious sign of a faulty power supply is when your computer won’t even turn on. Even if everything else on your computer is broken, if your power supply is operational its fan should turn and you’ll still see a power LED light up near the power supply or on the front of the case.

How can I test if my power supply is working?

How do I check my PC power supply with a multimeter?

Connect the negative probe on the multimeter (black) to any ground wired pin and connect the positive probe (red) to the first power line you want to test. The 24-pin main power connector has +3.3 VDC, +5 VDC, -5 VDC (optional), +12 VDC, and -12 VDC lines across multiple pins.