Abstract: A resonant protection kit for power supply is disclosed herein mainly comprising a circuit being adapted to perform analysis, determinative, and counter function. The circuit collects a divided voltage on a capacitor to calculate an effective voltage value and adopts fundamental and non-fundamental waveform manner to calculate an effective total current value of the capacitor. The circuit is selectively actuated to cut off the capacitor from a power system or adjust its impedance characteristic for protection if an abnormal voltage or current is sensed.