A method of monitoring a power factor correcting (PFC) power supply is provided. The method includes: powering on the PFC power supply with a constant current; starting a runtime counter that increments a count value; measuring an output voltage; calculating an output power by multiplying the constant current by the output voltage; storing the output power in a random-access memory (RAM); calculating an input power by multiplying the output power by an efficiency curve factor; and storing the input power in the RAM.