An example controller includes a delayed ramp generator, an integrator, an arithmetic operator, and a drive signal generator. The integrator integrates an input current sense signal representative of an input current of the power supply to generate an input charge signal. The input current has a pulsating waveform with a period that is a switching period of a switch of the power supply. The arithmetic operator circuit generates an input charge control signal responsive to the input charge signal and a ratio of a rectified input voltage to a dc output voltage of the power supply. The drive signal generator produces a drive signal responsive to the input charge control signal and a delayed ramp signal generated by the drive signal generator to control the switch.