Disclosed is an electronic apparatus including a connector configured to connect the electronic device to an external apparatus; and a power circuit configured to supply power to the connected external apparatus, the power circuit including: a transformer configured to output an output voltage by varying a level of an input voltage; a switching unit comprising a switch configured to perform switching operation for the transformer; a controller configured to control the switching unit to match a level of the output voltage with the external apparatus; and an auxiliary power circuit including an auxiliary winding, and configured to supply power to the controller based on a voltage induced in the auxiliary winding by the output voltage and to decrease the number of turns of the auxiliary winding based on the output voltage having a level greater than or equal to a predetermined value.