Voltages/Timings that Work with Certain Hardware

Desktop computers rely on their power supplies as primary sources of energy. To the untrained eye, a power supply can seem quite intimidating. Inappropriate wiring can be detrimental to your PC, with the possibility of burning up the power supply and motherboard. However, XOTIC PC provides almost 20 years of experience in computer hardware. In this guide, we explore the operating structure, the meaning of colored wires, and the relationship between voltage and current to output power.

Introduction to PC Power Supply

The power supply unit of a computer consists of several interior components, such as coils, capacitors, and electronic circuit boards to regulate current. Your power supply unit requires fans to cool down the interior components, but fans are one of the primary reasons for power supply failure. You will also find colored wires attached to the circuit board, and these wires are used to transmit various voltages to the main board and any connected devices. The typical PC power supply draws approximately 110 volts of alternating electrical current from the wall outlet, which converts to a much smaller unidirectional flow of electrical current.

Alternating current (AC) defines the flow of charge that changes direction periodically. AC voltage is produced by the alternator, which is a special kind of electrical generator used to produce alternating current. Direct current (DC) can be described as a constant voltage or current, which is generated by a rectifier, batteries, or an AC generator that is equipped with a commutator. Modern power supplies are equipped with several safety circuits that check the flow of current continuously to detect extreme power output conditions.

Computer Power Supply Voltages

There are three primary types of DC voltage. 12 Volts is required to feed the mainboard and any new-gen graphics cards. 5 Volts is necessary for the chassis and CPU fan or USB ports. 3.3 Volts is used to power the CPU. 12 Volts can also be applied to specific “smart” chassis fans. Power supply can convert to a 100 Volt electrical current to +12V, -12V, +5V, -5V, and +3.3 V. Your circuit board is used to forward any converted electricity through dedicated cable sets, so you can feed the components and devices within your computer. With the help of those components we listed above, AC voltage can be transformed into a clean direct current. PC capacitors are designed to regulate smooth, clean currents to the circuits of your computer. Negative voltages are relatively obsolete in the modern market, but you will want to know how to use them if you’re installing a new power supply in a system with an old motherboard that features ISA bus slots. Follow the general guide below to determine voltage rails.

  • +3.3 V: Chipsets, DIMMS, PCI/AGP/PCIe cards, and miscellaneous chips
  • +5 V: Disk drive logic, low-voltage motors, SIMMs, PCI/AGP/ISA cards, and voltage
  • +12 V: Motors, high0output voltage regulators, and AGP/PCIe cards

Power Supply Unit Color Codes

Manufacturers will typically provide specifications on request for their power supplies, but the typical 250-watt LPX and 235-watt ATX power supplies can be identified by the following parameters:

Black: Used to provide a ground for the current. Every other colored wire should be paired with a black wire.

Yellow: Used to denote +12Volt

  • 250-watt LPX: Maximum of 10 amps (120 watts)
  • 235-watt ATX: Maximum of 8 amps (96 watts)

Red: Used to denote +5Volt

  • 250-watt LPX: Maximum of 25 amps (125 watts)
  • 235-watt ATX: Maximum of 22 amps (110 watts)

Blue: Used to denote -12Volt

  • 250-watt LPX: Maximum of 0.5 amps (2.5 watts)
  • 235-watt ATX: Maximum of 1 amp (12 watts)

White: Used to denote -5Volt

  • 250-watt LPX: Maximum of 0.5 amps (2.5 watts)
  • 235-watt ATX: Maximum of 0.5 amps (2.5 watts)


  • 235-watt ATX: Used to denote +3.3Volt, or a maximum 14 amps (46.2 watts)

Green: Used to check DC voltage

Purple: Used to denote +5V on standby mode

If you have any questions about voltages and timings that work with certain hardware, please contact us today for additional information or further assistance. Let us know how we can help!