The direction of the current's flow is reversed, or alternated, on a regular basis in alternating current, while in Direct Current it flows in the same direction at all times. Most appliances in households run on AC power, however there are appliances which run on DC power. Such devices are generally powered by batteries. Most of these devices are power guzzlers and drain the batteries in a very short time; calling for frequent battery replacement. The solution for such a situation is to use rechargeable batteries, or draw power from the wall socket and use an intermediate device to convert AC power from the supply lines into DC power of required voltage.
This device that converts AC into DC of required voltage is known as AC Adapter. Most portable and semi-portable devices, which require DC, use adapters to get their power. AC adapters contain a rectifier which converts AC to DC and a transformer which converts voltage from 120V (supply line voltage) down to the required voltage. AC adapters are of two types; Regulated and Unregulated. In an unregulated AC adapter voltage output of the power supply floats with the load placed on them. Devices which are sensitive to input voltage should not use unregulated adapters as the device may get damaged. A regulated AC adapter ensures that the output voltage will always be constant.
When purchasing an AC adapter make sure that the output voltage and output current specification matches that of the device to which it is to supply power. The size of the output plug of the adapter varies. Ensure that the output plug is suitable for your application. Devices such as laptops, keyboards and digicams use AC adapters to get their power. The most common application of adapter is its use as a recharging device for cell phone batteries. | 
