External power adapters are a type of power supply that plug into a wall outlet and convert alternating current (AC) to a direct current (DC) that powers certain electronic devices. They may also be called AC adapters, AC-DC adapters, AC-DC converters, DC power supplies, external adapter power supplies, or simply power adapters. 

External power adapters are used in a variety of applications, from sophisticated medical devices like circulatory pumps, ventilators, dialysis equipment, and telemedicine carts, to commercial or industrial manufacturing equipment like barcode scanners, weighing scales, and assembly line monitors, to consumer devices like laptop computers, computer monitors and printers. 

You can think of an external power adapter as a “black box,” with the AC input on one side and the DC output on the other side. It is typically offered in one of two styles, depending on the application requirements: wall mount or desktop. A desktop power adapter is designed to sit on the floor or a desktop and is typically shaped like a brick and has a power cord sticking out of one or opposite ends. A wall-mount power adapter has only an output cord at one end and includes power blades that protrude from the body of its case to plug directly into an AC wall socket.

A wall mount power adapter eliminates the need for an AC input cord but is limited to being used with the style of AC wall socket specific to a particular country unless it has an option for interchangeable AC plugs. A desktop adapter may include a captive AC cord and plug, which would have a similar limitation to a wall mount adapter, but most use a standard AC inlet that can accept different AC cords with plugs specific to whichever country in which they will be used. 

Most external power adapters available today – both wall-mount and desktop – can accept a “universal” AC input voltage of 90 to 264 volts AC (VAC). This voltage range will support the vast majority of countries, with the need to match only the AC input cord or wall plugs for a specific country; the power adapter itself can be used universally. This feature results in supply chain efficiency, and may even result in reduced product costs by leveraging volume manufacturing.

The main reasons for a product engineer to use an external power adapter over an internal (“embedded”) power supply in their system are size reduction and ease of replacement. By using an external adapter, the product itself can be made smaller (although the power adapter itself adds size back to the complete system – no free lunches!) And an external adapter can easily be replaced by a user, without the need for support from an experienced technician. The user simply needs to ensure that they have selected an adapter that will work with their product.