Alternatively known as an AC/DC adapter, AC converter or charger, an AC adapter is an external power supply used with devices that run on batteries or have no other power source. AC adapters help reduce the size of a laptop computer by alleviating the need for a standard sized power supply. As shown in the image, an AC adapter is made up of a central unit which draws power from an AC outlet. It then converts the power to DC that's used by the computer, and a second cord that plugs into the computer.
Each AC adapter has a specific power rating, measured in volts or watts that it can handle and output to an electronic device. Because the power rating and type of plug is not universal the AC adapter can only be used with devices with the same requirements and connector.
If necessary, a universal AC adapter can be used, which is designed to work with many devices, having multiple types and sizes of plugs for connectivity to those devices. A universal AC adapter may also have a voltage or wattage range, like 100 volts to 240 volts or 70 watts to 125 watts, allowing for a greater range of compatible devices.