What is the function of PFC in power supply?

PFC stands for Power Factor Correction. The purpose of PFC is to improve the ratio of apparent power and real power.

The power factor is only 0.4~0.6 in non-PFC models. In PFC models, the power factor can reach above 0.95.

The calculation formulas are as below:
Apparent Power = Input Voltage x Input Current (VA)
Real Power = Input Voltage x Input Current x Power Factor (W)

From the environment-friendly point, the electric power plant needs to generate a power which is higher than apparent power in order to steadily provide electricity to the market. The real usage of electricity should be defined by real power.

Assuming the power factor is 0.5, the power plant needs to produce more than 2VA to satisfy 1W real power. On the contrary, if the power factor is 0.95, the power plant only needs to generate more than 1.06VA to provide 1W real power need. It will be more efficient.