Disclosed is a power supply including a first voltage generating unit that generates a first voltage from an external power supply; a second voltage generating unit that generates a first predetermined voltage and supplies the generated first predetermined voltage to the load; a third voltage generating unit that generates the first predetermined voltage and supplies the generated first predetermined voltage to the load; and a controller that causes the first voltage to be greater than or equal to a second voltage during a first mode, and causes the first voltage to be less than the second voltage during a second mode. During the first mode, the power is supplied from the second voltage generating unit and the third voltage generating unit to the load, and during the second mode, the power is supplied from the third voltage generating unit to the load.