Complete Guide to Desktop PC Power Supply Voltages and Wire Color Standards

Whether you're building a desktop PC or troubleshooting a power-related issue, understanding the different voltages and corresponding wire colors from your power supply unit (PSU) is crucial. When connecting high-performance graphics cards or storage devices, knowing which voltage supplies what component ensures both safety and system stability.


`A reference chart showing desktop computer power supply voltages and corresponding wire colors, including descriptions for each voltage's function in components like CPU, GPU, USB ports, and motherboard.`

In this post, we’ll break down the ATX PSU standard and explain each voltage, its function, and the associated wire color. This guide is designed to be beginner-friendly with practical examples to help you grasp how everything connects inside your PC.

 

 

 

Main Voltages and Wire Colors in an ATX Power Supply

  • +3.3V (Orange): Powers logic-level components like the motherboard chipsets and memory modules. Essential for stable data handling in modern systems.
  • +5V (Red): Used by legacy disk drives and many USB ports. Still common in today’s systems for peripheral devices.
  • +12V (Yellow): Delivers power to the CPU, GPU, cooling fans, and disk drive motors. One of the most powerful voltage lines, critical for performance parts.
  • -12V (Blue): Previously used for serial ports and ISA slots. Rarely used today except in certain servers or legacy hardware.
  • -5V (White): Supported very old ISA expansion cards. No longer part of modern ATX PSU standards.
  • GND (Black): Ground wire for all voltages. Vital for a stable and safe power flow.
  • +5VSB (Purple): Standby power. Supplies 5V even when the system is off, allowing functions like USB charging.
  • Power Good (Gray): Signals that the power supply is stable and ready.
  • PS_ON# (Green): Controls PSU power state. Pulling this line low (to ground) turns on the PSU.

 

 

Voltage and Color Codes in Auxiliary Power Connectors

  • CPU Auxiliary Power (4/8-pin): Supplies +12V (Yellow) and GND (Black) directly to the CPU for high-stability performance.
  • PCIe Auxiliary Power (6/8-pin): Feeds high-power GPUs. Also consists of +12V (Yellow) and GND (Black) wires.
  • SATA Power Connector:
    • Yellow: +12V
    • Red: +5V
    • Orange: +3.3V
    • Black: GND

Why Color Coding Matters

Wire color isn't just for visual convenience. It’s the language of hardware—essential for repair, customization, and safe wiring. Color coding allows for quick voltage identification, troubleshooting, and voltage measurement with a multimeter.

Especially for those modding power supplies or doing custom PC builds, knowing the function of each wire by color helps prevent damage, such as overvolting components or causing shorts.

 

 

Helpful Testing Tips for Power Supplies

  • PS_ON# Test: Connect the green wire (PS_ON#) to a black wire (GND) to manually turn on the PSU for testing purposes.
  • Using a Multimeter: Measure the voltage of each color-coded line to detect abnormalities. For example, if the +12V line drops below 11.4V, it could indicate a power issue.
  • Check 5VSB: After shutting down the system, the purple wire should still output 5V, confirming the standby power is functioning correctly.

Conclusion – Wire Colors Are the Language of Hardware

The voltages and color codes of power supply wires aren’t just technical trivia—they're critical indicators of your system’s health. Understanding these connections helps you build, upgrade, and troubleshoot your PC with confidence.

If you're planning to replace your PSU, build a new desktop, or simply curious about how power flows through your system, remember this guide—it might just save your hardware one day.