Free Sample
The Complete Handbook of Computer Power Supplies
Essential knowledge for professionals, businesses, and serious hobbyists who specify, deploy, maintain, or profit from computer power supplies
by Alumigogo Books
Chapter 1: Understanding Computer Power Supplies
A computer power supply is not a simple box that converts electricity from the wall into a form your computer can use. It is a precision instrument that must transform unstable AC (alternating current) from a utility outlet into stable, regulated DC (direct current) at multiple precise voltages simultaneously, under load conditions that change moment to moment, while dissipating significant heat, and protecting your entire system from electrical faults. Understanding what it actually does, and why design quality matters, is the foundation for making any competent decision about power supplies.
What a Computer Power Supply Does
Start with the utility power at your wall outlet. In North America, it's 120V AC at 60 Hz. In most of Europe and Asia, it's 230V AC at 50 Hz. This current alternates direction 50 or 60 times per second. Your computer cannot use this. It needs DC voltage—current flowing in one direction only, and at specific voltages that are stable and precise.
A computer power supply's primary task is to take that raw AC utility power and deliver multiple stable DC outputs. For an ATX power supply—the standard for desktop computers—those outputs typically include +12V (for CPU, GPU, and other power-hungry components), +5V (for motherboard logic and some legacy components), +3.3V (also for motherboard logic), -12V (a small negative rail for legacy circuits), and 5VSB (5V standby, for wake-on-LAN and similar features, even when the system is off).
The transformation happens in stages. First, the incoming AC