The power supply is an important part of an electronic system, whose reliability determines the reliability of the entire system. The secondary power supply in the servo system is prone to failure during its operational life cycle, resulting in no power output to the system. The electrical stress of a series of physical nodes is analyzed using the power supply model so as to clarify the potential failures in the supply. The practical measurement of the real power supply is also used to verify these given root causes. Moreover, the design defects are eliminated by modifying the circuit topology, so that the reliability of the power supply can be significantly improved.