Articles :: Power Supplies 101: A comprehensive guide ::

Jon Gerow · 06-26-2006 · Category: Guides

The PC power supply:

A PC power supply is, as the name implies, a means to deliver power to a PC. It takes AC from the wall outlet and converts it into DC of several different voltages.

Most of us use what is called an "ATX" power supply. "ATX" is a term coined by Intel to describe a power supply with several specific characteristics: Certain DC output voltages, certain number of pins on particular connectors and size. The size of an ATX power supply is 150MM wide, 86MM tall and is typically 140MM deep. Some power supplies of greater power or certain features, like modular interfaces, can actually be 155MM or deeper.

Before we dive into interpreting the label of an ATX power supply, we need to cover some preliminary terms...

Amps, Amperage or "A":

The strength of electrical current is measured in Amps. The larger this number, the more power that's available.


Volts and rails:

A volt is a standard unit of electrical potential. A PC power supply supplies several voltages to a computer. +3.3V, +5V, +12V, -12V and sometimes -5V. "Rails" is the name given to these individual supplies of voltages.



Watts is a standard unit of measurement derived from taking Amps and multiplying by Volts. That said, you can probably see how knowing the "wattage" of a power supply may not be enough since you have multiple rails, delivering different voltages, capable of different amperages and the total wattage is really just the sum of the capability of all of these rails. That leads us to the next part.....


  1. Introduction
  2. The PC power supply:
  3. The PC power supply label:
  4. Defining the connectors of an ATX power supply
  5. ATX power supplies DO NOT turn on at the flip of a switch
  6. Testing your power supply's voltage: Software vs. Multimeter
  7. Power Supply Efficiency
  8. The Derating Curve
  9. Power Factor Correction
  10. The resistance of modular connectors, adapters and splitters
  11. Conclusion

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