PC Mechanic - online guide to computer hardware 
Contains overviews, purchasing and installation information for PC motherboards, memory, drives, expansion cards, and power supplies. Also contains links to companies and manufacturers and PC hardware related links.
PC external power and power supply reference
A reference guide looking at the power systems of the PC from the inside and out. Covers electricity basics, power problems, UPSs, power supply functions, form factors, and sizing and output.
Power Supply Function and Signals
Describes AC-DC voltage conversion, different voltages supplied, the Power Good signal, and power loading. This page is part of "The PC Guide".
Troubleshooting Power Sources and Power Protection Devices
Lists some typical problems related to the system power, including external power problems, power protection devices (surge suppressors, UPSes, etc.) and the internal power supply. This page is from "The PC Guide."
Yahoo!'s power supply companies page
Yahoo!'s directory of power supply companies.
A Different Perspective on Power Supplies
With the latest system components putting ever-higher stress on a computer’s power supply, how do you know how much power your system needs? And with transformers, rectifiers, filters and voltage regulators to consider, how can you pick a good power supply?
