In this paper, in order to improve the in-series power decoupling circuit, an in-series and -parallel method is proposed to further reduce the extra capacitor without performance penalty. Based on DC-side in-series method and AC-side three-leg method, a novel way is given to not only reduce the DC-link capacitor but also to decrease the extra capacitor. Thus, it could further make the system high power density and long lifetime. Simulation results are presented to show the performance of this proposed method.