power factor correction and switched power supply efficiency
In the field of engineering, efficiency means thermodynamic efficiency, real output power divided by real input power. A power factor correction circuit reduces the efficiency of the equipment that contains the circuit but improves the overall system efficiency by reducing the RMS current required to transmit a given amount of real power.

In the case of switched power supplies, the power factor correction circuit improves the total power factor by reducing the harmonic distortion of the input power waveform. The benefit is partly reducing the current required, but perhaps more importantly, preventing the power supply from contributing to distortion of the voltage of the source power system.