A power supply and associated method include a power supply converter having a power output and configured to provide a supply voltage through the power output to a communications device. A simplified boost circuit is connected to the power supply converter in parallel but isolated from the power supply converter's bulk input capacitance during normal operation. The boost circuit includes at least one power storage circuit and a charging circuit connected thereto and configured to charge and maintain the power storage circuit to a predetermined voltage and switch the power storage circuit into the power supply converter during an undervoltage condition to transfer the stored power from the power storage circuit to the power supply converter and maintain the supply voltage to the communications device connected thereto for a required hold-up time.