The output filter electrolytic capacitor in the switching power supply has a sawtooth voltage frequency as high as tens of thousands of hertz, or even tens of megahertz. At this time, capacitance is not its main indicator. The standard for measuring the quality of high-frequency aluminum electrolytic capacitors is the “impedance-frequency” characteristic. It is required to have a low equivalent impedance within the operating frequency of the switching power supply, and at the same time, it has a good filtering effect on the high-frequency spike signal generated when the semiconductor device is working.