To meet the needs of the magnetic field accuracy of the Separated Sector Cyclotron (SSC), the main field power supply must be modified. We proposed a combination of switching power supply and linear power supply as the transformation solution of new power supply. There are two parts of the power supply, modular switching power supply is used as the front-end voltage source, and the triode linear adjustment circuit is used as the main circuit of the back-end module. Making full use of the advantages of these two kinds of power supplies, a power supply with high-stability and low-ripple current output was achieved, while the power density and reliability was greatly improved. The article introduces the principle and the reformation process of the power supply, elaborates the linear amplification principle of the triode, the design of the tube voltage drop control circuit and the output current control circuit. The power supply was verified through the simulation, and tested experimentally on the power supply prototype. The test results show that the stability of the output current after the reformation has reached ±3.99×10^-6, the current ripple has reached 2.7×10^-9, the performances are better than that before reformation.