The invention relates to a constant current source power supply. The power supply comprises a starting circuit, a pulse width control circuit, a rectification and filtering voltage sampling circuit, apower switch tube, a transformer, rectification and filtering circuits and linear voltage regulators, wherein the starting circuit is connected with a primary winding of the transformer through the pulse width control circuit and the power switch tube; the transformer is provided with a feedback winding, and the feedback winding passes through the rectification and filtering voltage sampling circuit and then controls the pulse width control circuit; the transformer is provided with multiple secondary windings, each secondary winding corresponds to a rectification and filtering circuit and a linear voltage regulator, and each secondary winding outputs a power supply through the rectification and filtering circuit and the linear voltage regulator. According to the invention, the feedback winding is designed, and secondary voltage regulator is carried out through the fed back output power supplies, thereby achieving high-performance output of the constant current source power supply, andsolving the problems such as low power conversion efficiency, serious heating of power devices and poor power supply voltage adjustment rate and load adjustment rate.