Red

Represents the +5V motherboard circuit and memory module power supply, Optical drive , Signal power supply for devices such as hard drives

Note: The number of +5V wires is comparable to that of the yellow wires. The +5V supply provides operating voltage to the CPU, as well as to integrated circuits such as PCI, AGP, and ISA devices, serving as the primary power source in a computer. Modern CPUs typically employ a hybrid power architecture using both +12V and +5V; their power‑supply requirements are no longer as stringent as in the past. However, the latest Intel ATX 12V 2.2 specification has enhanced the +5V rail’s current‑carrying capacity, particularly to better support dual‑core CPUs. The quality of the power supply directly impacts the overall stability of the system.

Yellow

Provides +12V power to the CPU and graphics card; also supplies power to standard drive circuits, such as those for optical drives and hard‑drive motors.

Note: The yellow wires are typically among the most numerous in a power supply. With the addition of power delivery to the CPU and PCI‑E graphics cards, the +12V rail plays a crucial role in the overall operation of the power supply.

Orange

The +3.3V rail is primarily used to power SATA hard drives, though it may have other applications in the future.

Explanation: This is ATX power supply A dedicated circuit supplies power to the memory. In the latest 24‑pin main power connector, the +3.3 V supply has been specifically reinforced. This voltage requires strict compliance: stable output, low ripple, and a high current capacity—typically 20 amperes or more. To ensure safety, many mid‑range and high‑end motherboards employ high‑power MOSFETs to regulate memory power delivery; however, improper insertion of the memory module can still damage these transistors. It operates at +2.5 V. DDR memory and +1.8V DDR2 memory On the platform, voltage conversion circuits are installed on the motherboard.

Purple

Provides +5V (USB) power to USB devices and supports the wake‑up function for USB keyboards and mice (continues to supply power even when the system is off).

Note: The ATX power supply supplies power to via PIN9. Motherboard Provides a +5V, 720mA power supply, which powers the WOL (Wake-up on LAN) and the power‑on circuitry. USB port The circuit provides power. If you do not use it… Wake-on-LAN When using such features, please disable them. Jumper wire By removing it, these devices can be prevented from drawing current from the +5VSB power supply. The quality of power supplied to this rail directly affects… Computer standby Yes, power consumption is directly tied to our electricity bills.

Black

Reference ground (0 V), an essential component of the power supply circuit.

Note: The ground wire of the system circuit.

Green

Represents the PS-ON power-on signal wire (which activates the power supply when shorted to ground).

Note: The power supply is switched on or off based on the voltage level at this pin. When the signal level at this pin exceeds 1.8 V, the main power supply is turned off; if the signal level falls below 1.8 V, the main power supply is turned on. Use a multimeter to measure the output voltage at this pin, which typically hovers around 4 V, as the pin outputs a voltage that corresponds to the input signal level. Here’s a simple, preliminary method for assessing whether the power supply is functioning properly: briefly short the green wire to any black wire using a piece of metal. If the power supply remains unresponsive, it indicates that the unit is defective. Many power supplies incorporate protection circuitry; when shorted without an external load, they will automatically shut down. Therefore, carefully observe the power supply’s behavior during its initial startup.

Gray

Represents the Power‑Good monitoring line, which connects the motherboard to the power supply and provides signal feedback.

Note: Under normal circumstances, if the output of the gray P‑OK line is above 2 V, the power supply can be used without issue. However, if the P‑OK output falls below 1 V, the power supply cannot guarantee proper system operation and must be replaced. This is also one of the primary methods for assessing a power supply’s lifespan and determining whether it meets specifications. Understanding the correspondence between the power supply’s output wires and their respective voltages helps us better grasp the device’s output specifications, which is particularly useful when selecting a power supply or troubleshooting power‑supply-related issues. Fault Time is very useful.

Blue

Representative - 12V vintage Serial port (Rarely used)

Note: The −12 V supply provides the logic‑level threshold for the serial port and requires only a small current, typically below 1 A. Even if the voltage deviates significantly, it will not cause a malfunction, since the logic‑0 level spans a wide range, from −3 V to −15 V.

White

-5V ISA bus (rarely used)

Note: Few commercially available power supplies come with a white wire. The white‑5V line is intended to provide a reference voltage for logic circuits and requires only a very small current; it typically does not affect normal system operation and can generally be omitted.