A power management system capable of outputting AC voltages includes a plurality of power units, at least a first diode, a first polarity switch unit and a control unit. The power units are electrically connected to form a power unit string. Each power unit includes a battery module and a first switch device connected in serial. One end of the first diode is connected to one of the power units, and the other end thereof is connected to a first common node to form a discharge path. The first polarity switch unit is electrically connected to the first common node and the power unit string, and outputs a first operating voltage. The control unit is electrically connected to the first switch device and the first polarity switch unit to turn on/off the first switch device and control the output polarity of the first polarity switch unit.