According to the power supply demand of a ground sampling equipment, an isolated single-power DC-DC module DPBL16-W24S5 and DPE75-24S12 chip are used to design a secondary power supply that converts the external power supply voltage of 27 V into 5 V and 12 V respectively and solve the problem of power supply voltage mismatch. The hardware circuit of power supply conversion is designed. Printed circuit board (PCB) design is conducted with Altium Designer software, which has higher anti-interference performance. And the output voltage is measured and the test results are summarized and analyzed. The circuit test results show that the power supply conversion circuit has stable output voltage and voltage stabilization precision.