At least one aspect is directed to an uninterruptible power supply that includes a first input having an input line connection and an input neutral connection to receive a first input voltage from a first voltage source, a second input to receive a second input voltage from a second voltage source, and a boost circuit configured to provide a positive output DC voltage with respect to the input neutral connection and a negative output DC voltage with respect to the input neutral connection in both a line mode of operation and a backup mode of operation. The power supply also includes a first connection circuit to couple the first input to the boost circuit in the line mode of operation, and a second connection circuit to couple the second input to the boost circuit in the backup mode of operation, the second connection circuit being configured to isolate the second voltage source from the input neutral connection in the line mode of operation.