Abstract: A power supply device with an electromagnetic compatibility heatsink, the power supply device has a circuit board, multiple electric elements and a housing and the electromagnetic compatibility heatsink has a shield and at lease one fin. The shield abuts the bottom of the circuit board and has at least one side edge. The at least one fin is formed on the side edge of the shield, extends up and touches the electric elements. When the electric elements converts alternating current to the direct current, electromagnetic waves and heat are generated. The heat is drawn from the electric elements to the fin and is conducted to the shield to dissipate and cool the electric elements. The shield blocks the electromagnetic waves and provides electromagnetic compatibility. The shield and the fin are formed together so the power supply device only needs one part improve electromagnetic compatibility and implement a cooling capability.