The Power Supply Unit (PSU)

Power Supply Units are to never be opened and worked on! They have enough stored voltage to stop a heart.

Is an internal computer component that converts high-voltage alternating current (AC) from a wall outlet into low-voltage direct current (DC) required by the computer's internal components. Despite its name, the PSU does not generate power; it acts as a converter and regulator, transforming raw electrical energy into stable precise voltages that the Motherboard, Central Processing Unit, Graphics Processing Unit and peripherals can safely use.

Core Functions:

• AC to DC Conversion - It takes the AC electricity from the mains (typically 110-120V or 220-240V depending on the region) and converts it into DC electricity, which is the only form of power computer chips can utilize.

• Voltage Regulation - Modern PSUs regulate the output to fine tolerances, ensuring a steady flow of power. This prevents voltage spikes or drops that could damage sensitive hardware like a $300 graphics card.

• Power Distribution - It distributes power across multiple voltage rails to different components:

  • +12V rail - Handles the bulk of the power for high-draw components like the CPU, GPU and case fans.

  • +5V and 3.3V rails - Power storage devices (SATA drives), USB ports and motherboard logic.

  • +5VSB (Standby) - Provides a small amount of power even when the PC is off enabling features like Wake-on-LAN.

Types & Standards:

• Switched-Mode Power Supplies (SMPS) - Almost all modern computers use SMPS technology because they are smaller, lighter more efficient and generate less heat than older linear power supplies.

• ATX Standard - Most desktop computers conform to the ATX specification, which defines the form factor, connectors and voltage tolerances. The most recent standard is ATX 3.1 (as of mid-2025).

• Efficiency Ratings - PSUs often carry efficiency ratings (80 Plus Bronze, Gold, Platinum) indicating how much energy is wasted as heat during conversion.

Wattage Requirements:

The required wattage depends on the system's use.

• Office PCs - Typically require around 300 watts.

• Multimedia & Entry-Level Gaming PCs - Often need 450-650 watts.

• High-End Gaming/Workstations - May require 750 watts or more to handle powerful graphics cards and processors.