According to one aspect, embodiments of the invention provide a UPS comprising a plurality of electrical buses, a first AC/DC converter coupled to the electrical buses and configured to convert a first input AC voltage to a plurality of DC voltages, a second AC/DC converter coupled to the electrical buses and configured to convert a second input AC voltage to the plurality of DC voltages, a third AC/DC converter coupled to the electrical buses and configured to convert a third input AC voltage to the plurality of DC voltages, a first DC/AC converter configured to convert the plurality of DC voltages into a first output AC voltage, and a DC bus balancer configured to maintain voltages present on the electrical buses by transferring energy between the plurality of electrical buses.