A resonant protection kit for a power supply includes a circuit adapted to perform analysis, determinative, and counter functions. The circuit collects a divided voltage on a capacitor to calculate an effective voltage value and uses fundamental and non-fundamental waveforms 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.