An AC Power Adapter is an electronic device which produces a specific direct current from the mains with an Alternating Current (AC). Although actually a power supply it is popularly known as an AC Power Adapter or AC Adapter. Laptops along with most other portable devices use Direct Current (DC), this also applies to rechargeable batteries which power laptops. Direct Current has a constant flow of electric charge in one direction and flows from low to high potential. Connecting a laptop to AC is unsuitable and dangerous due to the varying magnitude and direction of the current, which can cause an internal component to fail and even result in fire.
This is a particular design of a power adapter which accepts DC input and output DC voltage required to power a laptop. Instead of a standard plug for a wall socket, these have a specific cable that plugs in the cigarette lighter. The 12V DC supplied through the cigarette lighter socket is converted to provide a different DC voltage. This power adapter can also be used in other vehicles with similar sockets i.e. Vans, trucks and even boats. Air or airplane universal ac adapter
work in the same way.