Under normal circumstances, three transformers are arranged between the two heat sinks of the power supply, and the main transformer is the largest one; the medium “body” one is usually responsible for +5VSB output, and the smallest one is generally used for PWM The control circuit is mainly used to isolate the primary side and the secondary side part. Some power supplies do not use transformers as “isolators”, but use one or more optocouplers (looks like IC integrated chips), which means that the power supply using this design has only two transformers—— main and auxiliary transformers.