A power supply device for a display device and method for driving the power supply device are disclosed. In one aspect the device includes a power voltage selector configured to select at least one of a plurality of predetermined voltage values according to a power voltage control signal and output the selected predetermined voltage value. The device also includes a power voltage supplier configured to supply a power voltage corresponding to the selected predetermined voltage value to a display data processor and a controller configured to generate the power voltage control signal based at least in part on a change in a number of switched data bits defined as a data change degree. The controller is also configured to transmit the power voltage control signal to the power voltage selector. The data bits are configured to be switched substantially synchronously with a clock signal.