Generally speaking, the commonly used low-voltage AC switching power adapter directly rectifies the 220VAC power into an AC voltage of about 300V after passing through the EMI filter, and controls the switch tube to conduct high-speed on and off through the circuit, and then converts it into high-frequency AC power for the transformer. Transform the voltage to generate one or more sets of voltages required, and then rectify them into AC power of the required voltage.
The AC-DC switching power adapter chip (or module) can be made into a basic switching power adapter as long as it is matched with some RC components and a switching transformer.

The main working principle of an ordinary half-bridge switching power adapter is that the switches of the upper bridge and the lower bridge (the switch is VMOS when the frequency is high) are turned on in turn. First, the current flows in through the upper bridge switch, and the storage function of the inductance coil is used to convert the energy. It is accumulated in the coil, and finally the upper bridge switch is turned off, the lower bridge switch is turned on, and the inductor coil and capacitor continue to supply power to the outside. Then turn off the lower bridge switch, and then turn on the upper bridge to allow the current to enter, and so on. Because the two switches are turned on and off, it is called a switching power adapter.
As a switching power supply IC in AC-DC power adapters. The main advantages of AC-DC switching power adapter:
a: Small size and light weight (volume and weight are only 20% to 30% of the linear power adapter);
b: High efficiency (usually 60% to 70%, while the linear power adapter is only 30% to 40%).
It has strong anti-interference, wide output voltage range and modularization.