The present invention provides a power supply device which comprises a power transistor, a detection circuit, and a driving circuit. The power transistor is controlled by the driving circuit to generate output current. The first end of the power transistor is coupled to a power supply voltage pin through a first bonding wire. The second end of the power transistor is used for outputting the above current. The detection circuit is coupled to the two ends of the first bonding wire to detect the output current and generate a control signal. The driving circuit generates a driving signal according to the control signal. When the output current value is larger than or equal to an overcurrent protection current value, the driving circuit starts the adjust the voltage value of the driving signal such that the output current value is maintained at the overcurrent protection current value. The accuracy of the output current is improved.