This study presents a systematic approach for power-aware design of an optimized capacitive vibration energy scavenger. The proposed method is based on the mechanical domain impedance analysis. First we investigated the mechanical properties (impedance) of the capacitive transducer/conditioning circuit block. We found that this impedance depends strongly on the energy state of the conditioning circuit. From this conclusion we derived a method allowing to find the conditioning circuit operating mode (voltages on the capacitors) maximizing the power yield for a given resonant MEMS transducer block, a given conditioning circuit and given external vibration parameters. This method was successfully applied on the system composed from a charge pump and an inductive flyback circuit. The study was validated by behavioral modeling in VHDL-AMS language environment.