Abstract: During the charging period of capacitor charging power supply, the input power gradually increases with the increase of output voltage, which not only requires the power grid to provide a larger peak power, but also causes larger current harmonics. This paper proposes a new control algorithm based on a single-stage charging scheme with buffered energy storage capacitor that realizes the function of constant power input and constant current output only by using single-stage energy conversion. The algorithm not only achieves better constant power characteristics, but also lifts the restriction on the auxiliary energy storage capacitor. It can improve the equivalent excitation voltage by controlling the voltage of the energy storage capacitor. Matlab/Simulink was used to build a simulation model of capacitor charging with constant power input. The simulation results show that the constant power at the input end is realized during the 400−2 000 V stage of capacitor charging, the initial voltage of auxiliary capacitor is increased, and the voltage of load capacitor is increased at the same time. This shows that the algorithm can achieve better input constant power characteristics and circuit boost function.