This kind of power socket with USB charging port has an isolated AC-DC module inside, which directly converts AC 220V voltage to DC 5V voltage to charge mobile phones and other devices, the principle is the same as that of mobile phone charger, but the quality of AC-DC conversion circuit inside some sockets is not as good as that of mobile phone charger, and the charging current is slightly larger. It may heat up and reduce the output voltage, thus slowing down the charging speed.
The output voltage of the USB charging port above a power socket is measured by a USB voltmeter. When unloaded, the output voltage is measured at 4.97V.
The USB socket structure is generally composed of a socket shell, socket base, plug contact piece, connecting wire and circuit board. The plug contact piece is usually made of metal and is used to transmit signals and power in contact with the USB plug. A circuit board and cable are provided inside the socket base for electrical connection of the USB interface. The socket housing protects and holds the socket in place. The USB socket is simple, compact and easy to use, and has become one of the interface types widely used in modern electronic devices.