According to one aspect, embodiments of the invention provide a UPS comprising an input to receive input AC power, a bus configured to receive backup DC power, a first output configured to provide an output AC voltage derived from at least one of the input AC power and the backup DC power, a second output configured to provide an output DC voltage derived from at least one of the input AC power and the backup DC power, a first inverter coupled between the bus and a first transformer, the first transformer coupled to the input, a second inverter coupled between the bus and a second transformer, the second transformer coupled to the first output, and a controller configured to operate the second inverter to maintain the output AC voltage above a first threshold value and to operate the first inverter to maintain the output DC voltage above a second threshold.