PFC (power factor correction; also known as power factor controller) is a feature included in some computer and other power supply boxes that reduces the amount of reactive power generated by a computer. Reactive power operates at right angles to true power and energizes the magnetic field. Reactive power has no real value for an electronic device, but electric companies charge for both true and reactive power resulting in unnecessary charges. PFC is a required feature for power supplies shipped to Europe.
In power factor correction, the power factor (represented as "k") is the ratio of true power (kwatts) divided by reactive power (kvar). The power factor value is between 0.0 and 1.00. If the power factor is above 0.8, the device is using power efficiently. A standard power supply has a power factor of 0.70-0.75, and a power supply with PFC has a power factor of 0.95-0.99.
PFC is not used solely for computer power supplies. In other industries, PFC equipment is used to reduce the reactive power produced by fluorescent and high bay lighting, arc furnaces, induction welders, and equipment that uses electrical motors.