Filter capacitors play a very important role in switching power supplies. How to correctly select filter capacitors, especially the selection of output filter capacitors, is a problem that every engineer and technician is very concerned about. The common electrolytic capacitor used in the 50 Hz power frequency circuit has a pulsating voltage frequency of only 100 Hz, and the charging and discharging time is on the order of milliseconds. In order to obtain a smaller pulsation coefficient, the required capacitance is as high as hundreds of thousands of microfarads. Therefore, the goal of ordinary low-frequency aluminum electrolytic capacitors is to increase the capacitance. The main parameters of its advantages and disadvantages.