A power supply apparatus and a method for controlling the power supply apparatus are provided. The power supply apparatus drives an electronic apparatus which may operate in a first mode or a second mode. The power supply includes an input voltage generator that generates an input voltage; an output voltage generator that generates a first output voltage by using the input voltage, and supplies the output voltage to the electronic apparatus; and a detector that determines the mode of the electronic apparatus by detecting a load of the electronic apparatus, and outputs a control signal to the output voltage generator in response to the mode of the electronic apparatus changing from the first mode to the second mode. In response to receiving the control signal, the output voltage generator generates a second output voltage that corresponds to the second mode.