Power Supply Units

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The power supply unit (PSU) delivers direct current (DC) low voltage power to the PC components.

• PSU contains:
  • a rectifier to convert alternating current (AC) building power to DC voltage output
  • transformers to step down to lower voltages
  • and filters and regulators to ensure consistent output voltage levels
  • a fan, which dissipates the heat generated
• power supply’s size and shape determine its compatibility with the system case
  • available room, screw and fan locations
• form factor also determines compatibility with the motherboard
  • in terms of power connectors
• Most PSUs designed for use with desktop PCs are based on the ATX form factor
• A PSU is plugged into an electrical outlet using a suitable power cord
  • Before doing this, ensure that the PSU is compatible with the input voltage from the outlet
  • in North America, the input voltage is 120 VAC (low-line)
  • in UK, the voltage is 230 VAC (high-line)
  • not cross-compatible
  • facilities such as data centers typically use high-line voltage because it is more efficient
• Most PSUs are dual voltage and are auto-switching
  • some have a manual switch to select the correct voltage
  • fixed voltage types can only accept either low-line or high-line
• input operating voltages should be clearly marked on the unit and accompanying documentation