Power supplies have recently begun to push the limits of house hold electrics (wiring, circuit breakers etc.) and they also have begun to gain in the fields of efficiency.

There are many different ways to increase efficiency, with the usual being better components and the like. However, there is an obvious route to take in increasing efficiency. That is to use either an active or passive PFC.

PFC stands for power factor correction which is more technical that it first seems. As the input voltage for any household device is AC (alternating current – better than DC at distance power transmission) a PC power supply must convert this to DC.

As it is essentially an AC device it is subject to a power factor which can range between 0 and 1, with 1 being the ideal figure as it means that power is not being wasted by the device. A low power factor is indicative of a low efficiency device and vice versa.

In order to achieve the ideal of 1, you must use a PFC device, which is either passive or active. Passive methods are cheaper but generally only consist of capacitors which absorb wasted power in order to return it to the system when required. This has a side effect of creating unwanted harmonics on the output frequency which can have an impact on the stability of the device, which is key for a power supply which has to maintain a precise output DC voltage. Also, they are not as efficient as their active counterparts. If a passive method is used, a filter must then be used to remove the harmonics for better output voltages and stability.

The other option which is generally more expensive is an active PFC which most power supplies employ. This is a method of measuring the load on the device and creating the ideal situation and generating a power factor closer to 1. These devices are very efficient if done correctly and can reach very close to the ideal (for example, a SilverStone Strider 1000W PSU manages a PFC greater than 0.95 at full load).

A PFC is not necessary in a power supply, and never has been. However, having a low power factor will mean that you will end up spending more in the long run in regards to your electricity bill and thanks to the competition in the market, it’s now reasonably inexpensive to pick up a power supply with at least a passive PFC installed.