An AC adapter allows a battery operated device to operate or charge using regular AC current. DC power, or direct current is provided by batteries. AC, or alternating current is the type used by a house. Plugging a DC device into an AC outlet without an adapter is an invitation to disaster. An AC adapter has a plug that inserts into the device, and an inverter that plugs into a standard AC outlet. The inverter "changes" the current into DC current the device can then use safely.Battery operated devices such as radios, portable TVs, cassette and CD players are sold with AC adapters. If not used regularly, these items can be lost over time. They can also become damaged, or wear out. Look at the back of the device to see what the voltage and wattage is. Locate the adapter outlet and write down any numbers found there. These will help the user locate a replacement adapter.Electronic stores have salespeople well- trained to help locate the right equipment for the customer. Sometimes they will ask the customer to bring the device in so the correct adapter can be chosen. This is a wise decision to make.An online search may be conducted with success, but if the customer is unsure whether or not an adapter will work correctly, buying one that looks "close enough" may prove expensive with returns and exchanges.Cell phone chargers are an excellent example of an AC adapter. These, too can be lost, damaged or wear out over time. If the user has the old one, taking it and the phone to the provider's store often yields the correct placement. If the phone is no longer manufactured and batteries are still available, it may be worth going to an electronics store for a replacement.Universal AC adapters are sold to help reduce the frustration of searching for replacements. These adapters typically have four different plugs on one end so they can be used in a variety of devices. This reduces the need for multiple adapters and saves money with the purchase of a single device. By using the right adapter, any DC device can work or charge safely.