A power system is disclosed. Output terminals of a power supply or a DC-to-DC unit are cascaded to increase an output voltage, so as to reduce a current between the power supply or the DC-to-DC unit and the DC-to-AC unit, and resolve cost and loss problems of the cable from the power supply or the DC-to-DC unit to the DC-to-AC unit. In addition, according to the power system provided in the embodiments of this application, a quantity of cables from the power supply or the DC-to-DC unit to the DC-to-AC unit may be further reduced by cascading output terminals of the power supply or the DC-to-DC unit and cascading inputs of the DC-to-AC unit, thereby reducing system costs. In addition, in the power system provided in the embodiments of this application, cascaded input and isolated output of the DC-to-AC unit can reduce a specification of a power conversion device.