Power factor is the relationship between working (active) power and total power consumed (apparent power). The ratio of true ac input power to the apparent ac input power. Essentially, power factor is a measurement of how effectively electrical power is being used.

A higher power factor represents a more effective use of electrical power. Power Factor Correction on a switching power supply controls the timing and wave shape of the input current drawn to maintain the current waveform approximately in phase with and of the same shape as the line voltage.

This results in a power factor of approximately 1.0. This is important when electronic equipment consumes a significant amount of power, since otherwise the facility power system could exceed its current ratings for the power consumed and potentially impact other equipment on the same power system.