How-To Geek

Power Supply Unit (PSU)

The Power Supply Unit (PSU) is one of the most critical components of a computer system. The PSU is responsible for converting the mains AC (the power from the outlet) into low-voltage and properly regulated DC power for the hardware components of the computer can safely utilize. Manufacturing defects in a Power Supply Unit can have catastrophic consequences for the attached hardware.

Modern Power Supply Units adhere to the ATX standard developed by Intel in the 1990s and include positive rails–PSU power leads are referred to as rails–in 3.3V, 5V, and 12V packages to supply power to various components like the motherboard, video card, and drives.

The two most important numbers consumers need to be aware of when shopping for a PSU are the power rating (denoted in wattage, such as 600w) which indicates how much of a load the PSU can handle and the efficiency rating (denoted by percentage, such as 85%, or by a PLUS certification) which indicates how efficiently the PSU converts AC power to DC power. For more information about power ratings and efficiency, check out: What Exactly Does the Wattage Rating on a Power Supply Unit Mean?

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