ATX Power Supply Guide

Key Features of Power Supplies

Active or Passive PFC

PFC stands for Power Factor Correction and describes a way of reducing the difference between reactive power and active power within the electrical system. An active PFC usually refers to a circuit that controls the amount of power drawn to obtain a power factor that is close to unity. Active and passive PFCs directly benefit the electrical grid by increasing the effectiveness of the supplied power that is put to use. While not having a direct benefit to the consumer, PFC circuits in computer power supplies help the environment and are a required component to comply with some international laws. One benefit of an active PFC is that it is compatible with many input voltages between 90-260V and can work effectively in a power grid with a fluctuating energy supply. Power factors measured in these power supplies are between .65-.75 for passive PFCs and as high as .97-.99.

ATX V2.2

The latest ATX 2.2 standard brings many advantages over previous standards. For a modern computer, look for power supplies supporting the latest ATX V2.2 features.- 24-pin motherboard power connection with PCI-Express Support- 8-pin EPS12V and ATX12V connections- Dual or multiple 12V rails supplying over 18A per channel- Required SATA power connections- Minimum Efficiency of at least 70% with 80% recommended


Efficiency has a direct benefit to the consumer by lowering electricity bills. Efficiency measures the difference between the power input and the power output inside a computer system. The higher the efficiency of a power supply, the more power it can deliver relative to its listed wattage. High efficiency power supplies waste less power as heat energy and can be made quieter. According to ATX V 2.2 standards, power supplies must deliver 70% at full load, 72% at typical load (50%) and 65% at light (20%) load. True high efficiency power supplies have efficiency greater than 80% and even higher than 85% efficiency.

Low Noise

Most power supplies need constant cooling from a 80mm, 92mm, 120mm or 140mm fan or fans inside the unit. Reduction of noise in a power supply can reduce the overall noise of a computer and create a better computing experience. A low noise power supply has a built in fan controller that adjusts the cooling fans RPM based on internal temperature. Quietness is also based on the quality of the fan itself. As a general rule, a power supply will be less noisy the larger the fan it has. Also larger fans can cool more than smaller fans with less RPM. We recommend a power supply with at least 400W with high efficiency and a 120mm fan for the least amount of noise.


Reliability is the most important characteristic of a power supply. Usually reliability is measured in MTBF (Mean Time Before Failure). 50,000-100,000hrs is a common range and means that in manufacturer testing, half of the power supplies exceed that number and half will fail before the stated hours. A power supply with an MTBF between 100,000 and 400,000hrs offers excellent reliability. Some power supplies have a "Hi-Pot Tested" label. This test measures that if a power supply is exposed to a critical high voltage discharge, it will not pass this charge to the devices it powers.


Modular power supplies have easy to disconnect power cords. These cables can be removed from the power supply to minimize clutter in a case. These power supplies can also be called cable management and are a great way to have an organized system.

SLI Certified or Crossfire Certified

This label assures that the power supply can run the minimum specifications for SLI or Crossfire dual graphics cards. This type of power supply will have at least 2 dedicated PCI-e connections that can supply at least 18A total in each channel. Even with a SLI or Crossfire label, graphics cards have different power requirements so it is important to match the exact power requirements with the available power supplied.