A PFC equipped power supply may not affect the overall wattage performance but it allegedly makes the power supply more efficient at managing a stage of converting AC into DC and therefore reduce energy costs.

PFC makes the amps less "peaky," which helps power companies because their wiring has to be capable of carrying the peak amps, and with PFC they can deliver more power without increasing the peak amps. Commercial electric customers are billed according to PF, but, at least in the U.S., residential customers are not, so PFC won't cut their costs. The only benefit PFC gives them is the ability for their UPS to deliver more power (notice they're rated by VA, which is equal to power with a PF of 1). PFC actually reduces efficiency and raises cost of operation a very slight amount.