Standard power supplies draw line current in pulses around the peaks in line voltage. This may be undesirable for several reasons. PFC (Power Factor Correction) circuits ensure that the line current is drawn sinusoidal and in phase with the sinusoidal line voltage. This reduces the harmonic distortion of the power supply and increases the useful power drawn from the mains.  Power Factor Correction in a power supply can reduce electric utility bills, increase system capacity, and improve voltages.