A method of providing an auxiliary power by an auxiliary power supply. The method may include converting an external power to a plurality of charging voltages; charging a charging circuit with a first charging voltage of the plurality of charging voltages; monitoring a voltage of the charging circuit; when capacitance of the charging circuit is less than a first reference capacitance, charging the charging circuit with a second charging voltage of the plurality of charging voltages, the second charging voltage being higher than the first charging voltage by a first voltage amount; and providing an auxiliary power to outside the auxiliary power supply. The auxiliary power may be generated based on the voltage of the charging circuit.