The technology described herein is directed to a DC input power supply unit with an auxiliary boost control circuit (or controller) that facilitates continuous supply of power to a standby output load of the power supply unit in a bootloader mode. More specifically, the auxiliary boost circuit (or controller) is configured to assume control of a primary power boost stage from a primary controller in a bootloader mode so that the power supply unit can continue to supply power to the standby output with a protection function regardless of the state of the power supply unit or primary controller.