How Does a Power Supply Work?

The power supply unit converts power from the 115V AC normal wall outlet into DC current at much lower voltages that the computer can use. Most modern power supplies have switches to accomodate other voltages, such as the 230V standard used in Europe and elsewhere. Whether you're curious about the power supply your computer is using, or looking to purchase a new power supply, there's a few things to consider.

First, every power supply is rated in Watts. Most power supplies run between 400 to 800 Watts, with smaller power supplies for small computers and laptops and larger power supplies for high end machines. The largest power supply I've seen readily available rates at 1500 Watts. The wattage that you need in a power supply is directly related to what your computer has inside of it.

A standard computer will use around 120 Watts for the processor, 20-30 Watts for the main motherboard, and 20 watts per hard drive. If the computer has a built in graphics card, that will use around 70 watts. Seperate graphics cards that go in either the PCI-E slot or the AGP slot tend to use the most power, with wattages ranging from 70 watts all the way up to 450 watts for the graphics card alone! Once you add all of this together, you can see that a standard computer with a built in graphics card will typically use 240-250 watts. So why did I say that most power supplies start at 400 Watts?

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