Your computer's power supply is the most important part of the machine, as it provides a steady stream (or torrent, as the case may be) of power to your components. If your power supply isn't up to snuff, it may kill your expensive CPU or video card.
Protect your components against this with the Thermaltake Dr. Power PSU Tester. This inexpensive device allows you to test the motherboard connector, molex connectors, P4 connector, SATA connectors, and floppy connectors. It also loads up the 3.3V, 5V, and 12V rails. This tester is compatible with new 24-pin ATX connectors as well as the older 20-pin connectors.