What is an AC Adapter?

M.R. Anglin

Alternating current (AC) adapters are used to power or charge many common electronic devices, such as mobile phones, laptop computers, or external hard drives. An AC adapter changes AC power from an electrical outlet into the type of power or voltage that an electronic device needs to work. Typically, each device has a designated adapter that is pre-set to the proper voltage conversion. For this reason, among others, adapters generally are not interchangeable.

An AC adapter is used to transfer electricity from a wall outlet to a electronic device, such as a cell phone.
An AC adapter is used to transfer electricity from a wall outlet to a electronic device, such as a cell phone.

If a device does not have its own supply of power, it likely has to use an AC adapter in order to get power from the electricity mains of a building. An adapter is a type of power supply — a device that provides power to another device — and is used with cell phone chargers or the power cords for gaming systems, for instance. The large block that plugs into the wall is the power supply that converts AC power to the appropriate form for the device. Other names for this type of adapter include a plug pack or a wall wart.

A socket designed for use with AC electricity.
A socket designed for use with AC electricity.

Another place one may find a power supply is in a laptop charger or the power cord for a printer. In order to keep the power supply from taking up space on a wall and blocking other outlets, some AC adapters have their power supplies in a "brick" that lies on the floor. This brick-in-line configuration allows for the actual plug to be a normal size to allow more room at the wall outlet. These adapters often have nicknames, such as power bricks.

Having an adapter to power a device allows for several advantages to the device and its manufacturer. For example, heat and electronic interference are kept away from the device that is being powered. The device can also get the power it needs without having to generate its own electricity. In addition, the manufacturer can market the product throughout the world since all he needs to do is include or sell the correct adapter for the country in which the device is being sold or used.

One of the drawbacks to an AC adapter is that they oftentimes can be difficult to replace. If the adapter from a laptop is misplaced, for instance, an adapter from another type of laptop generally cannot be used to replace it. To offset this difficulty, some manufacturers have developed universal adapters. They come with a switch so a person can choose the appropriate voltage as well as interchangeable tips so he can choose the correct one for his device.

Hairdryers are usually plugged in using an AC adapter.
Hairdryers are usually plugged in using an AC adapter.

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Discussion Comments


@cardsfan27 - Good advice. I don't think I ever realized how much the cords actually cost. I think I'll look into buying a backup now.

Something else that I would suggest people buy even if you don't think you will ever need it is an AC car adapter. A friend got it for me as a gift, and I didn't think I would need one either, but it has saved me a couple of times.

One time, I had car problems, and I was kind of our in the middle of nowhere. Not surprisingly, my phone happened to have died right before that. Lucky for me, I had that adapter and my phone charger, so I could make a couple of calls to have someone help me. Since that time, I've just gotten an AC adapter cord that plugs right into the phone itself.


If you own a laptop, I would highly suggest buying a laptop AC adapter to keep as a backup. Over the past two years, I have had two instances where I had to replace my laptop cord.

In the first case, I got a new puppy, and he decided he wanted to chew on the cord one time when I was gone. Luckily, I had remembered to unplug the cord before I left, so he didn't get hurt. That time wasn't too much of a problem, because I had a friend with a spare cord that he let me have.

Just recently, though, I was traveling and left my cord behind at a hotel. By the time I realized it was missing, I was already back home. Stores realize that if you don't have a power cord to your computer that you are probably desperate to get one. For that reason, the price of notebook AC adapters in stores is outrageous. Fortunately, I had a backup computer I could use for a week. Meanwhile, I ordered a replacement adapter online for 25% of what they were selling them in stores.


@jcraig - The main job of the adapter is to convert the voltage of the wall outlet to a level that is acceptable for the device you are using. All standard wall outlets have a 120 volt charge. That is way too much for most devices, though. If you had 120 volts of charge going into a phone, it could end up ruining the circuits and battery. I don't know if the reverse of that is true or not, though. I'm not sure if some things actually increase the voltage of the wall outlet or if that is not allowed by various regulations.

The AC adapter can also convert the AC power into direct current that is more useful for most devices. Like you, I don't remember enough from my physics class to remember why direct current is used in different electronics. I just know that the electricity flows in one direction rather than back and forth like with alternating current.


Don't different countries have different types of AC outlets? I seem to remember seeing that on TV one time.

Whenever you have an AC adapter, what exactly does it do inside the little box or brick? I know that somehow it turns the AC power from the wall into a form that an electronic device can use, but why can't the electronics use the AC power straight from the wall? I remember too from physics class that there is direct current, but I don't remember what it does. Do the adapters somehow have something to do with converting from alternating current to direct current?

It seems like the electronics we use would be a lot more efficient if they didn't need that box taking up room by the outlet.

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