A power supply device includes two or more power supply units connected in parallel with each other, each of which includes a rectifier for converting DC power from a DC power source or AC power from an AC power source into predetermined rated DC power. The device further includes a sensor for detecting a load current rate of each of the power supply units, and a controller. The controller controls the operation of the power supply units to reduce the total amount of power consumption per power supply unit calculated based on the rated DC power and the efficiency of each of the power supply units corresponding to the load current rate. As a result, the power consumption of the power supply device can be reduced more appropriately according to the load state and the efficiency of the power supply units.