With the in-depth study of particle accelerator physics experiments, the requirements for higher beam quality have gradually increased. To obtain a magnetic field environment with extremely high stability and extremely low noise, a high-precision DC excitation power supply combining switching mode and linear mode was analyzed and designed. The front-end switching power supply provides a stable power source, and the back-end linear power supply is connected in series to control the linear amplification of the current for output. Based on the control loop of power supply current and tube voltage drop, the stability of the output current has been further improved through temperature compensation measures for key components. Through the modular design of the back-end linear power supply, the volume of the power supply has been reduced and the convenience of operation and maintenance has been improved. The measured results show that the long-term current stability for 8 h reaches 1.3×10^-6, and the noise is extremely low.