As an electrolytic capacitor for output filtering in a switching regulated power supply, the frequency of the sawtooth wave voltage is as high as tens of kilohertz or even tens of megahertz. Its requirements are different from those used in low-frequency applications. The capacitance is not the main indicator. The good or bad is its impedance-frequency characteristic, which requires it to have a low and equal impedance in the working frequency band of the switching regulated power supply. Spike noise can also have a good filtering effect. Generally, the impedance of ordinary electrolytic capacitors used at low frequencies is about 10 kHz, and its impedance begins to show inductance, which cannot meet the requirements of switching power supplies.