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IT Support & Hardware · Foundational

Power Supply Unit (PSU)

The component that converts AC wall power to regulated DC voltages for computer components.

Definition

A PC PSU supplies +12 V (CPU, GPU, drives), +5 V, +3.3 V, and +5 V standby rails. It is sized by wattage and efficiency rating. Symptoms of failure include no power, random reboots, and burning smells. PSUs contain high-voltage capacitors and should be replaced, not opened.

Example

Choose an 850 W ATX 3.1 PSU for a system with a 300 W GPU and 125 W CPU.

Exam tip

Never open a PSU for repair; capacitors can hold a dangerous charge even when unplugged.

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