A power supply for an ion engine comprises a multiphase alternator and a power converter comprising a voltage multiplier coupled to each phase of the alternator. Each voltage multiplier comprises one or more staged voltage doublers. The alternator phases may be coupled to each other in a Y configuration such that no common return line is required, and each phase of the alternator provides equal amounts of constant power in a balanced, sequential flow. The converter corrects for the alternator's inherent internal reactance, thereby minimizing the required output of the alternator and reducing the overall power required of the system. A controllable impedance can be inserted into a low voltage portion of the multiplier for selectably varying the output voltage and power of the supply.