A power module is a power supply that can be directly mounted on a printed circuit board. Its characteristic is that it can provide power for specialized integrated circuits (ASICs), digital signal processors (DSPs), microprocessors, memory, field programmable gate arrays (FPGAs), and other digital or analog loads. Due to the many advantages of modular structure, modular power supplies are widely used in communication fields such as switching devices, access devices, mobile communication, microwave communication, optical transmission, routers, and automotive electronics, aerospace, etc. Generally speaking, this type of module is called a Point of Load (POL) power supply system or a Point of Use Power Supply System (PUPS). Due to the many advantages of modular structure, modular power supplies are widely used in communication fields such as switching devices, access devices, mobile communication, microwave communication, optical transmission, routers, and automotive electronics, aerospace, etc. Especially in recent years, due to the rapid development of data business and the continuous promotion of distributed power supply systems, the growth rate of modular power supply has exceeded that of primary power supply. The module power supply has isolation function, strong anti-interference ability, and built-in protection function, making it easy to integrate. With the widespread use of semiconductor technology, packaging technology, and high-frequency soft switching, the power density of modular power supplies is increasing, the conversion efficiency is becoming higher, and applications are becoming simpler. In the field of switching power supply technology, people are developing related power electronic devices while developing switching frequency conversion technology. The mutual promotion of the two promotes the development of switching power supply towards light, small, thin, low noise, high reliability, and anti-interference with a growth rate of over two digits each year. Switching power supplies can be divided into two categories: AC/DC and DC/DC. DC/DC converters have now achieved modularization, and the design technology and production process have been mature and standardized both domestically and internationally, and have been recognized by users. However, the modularization of AC/DC, due to its own characteristics, encounters more complex technical and manufacturing problems in the process of modularization. The structure and characteristics of two types of switching power supplies are explained below