A wireless power receiving device may have wireless power receiving circuitry with a coil and rectifier. The wireless power receiving circuitry receives wireless power signals and uses the rectifier to supply a corresponding output. The output is characterized by a current, a voltage, and a power equal to a product of the current and voltage. The output of the rectifier is supplied to a direct-current-to-direct-current power regulator integrated circuit, which supplies direct-current power to a system load and battery. A controller integrated circuit directs the power regulator circuit to dither the current while monitoring for a peak in the power. If the power regulator circuit dithers the current satisfactorily, the wireless power receiving circuitry may be operated at the peak power. If the power regulator circuitry does not dither the current in response to being directed to dither the current, a wireless power transmission level may be reduced.