Editing AC adapter (section)

==Universal power adapters==
{{See also|DC connector|Coaxial power connector}}

[[File:Dcxconnector.jpg|thumb|A six-way connector on a "universal" DC power supply, consisting of a four-way X connector and two separate individual connectors (one is the [[nine-volt battery]] connector). The X-connector here provides 3.5 and 2.5&nbsp;mm [[Phone connector (audio)|phone plugs]] and two sizes of coaxial power connector]]
[[File:Ac adapter.jpg|thumb|Universal laptop power supply with adjustable voltage between 12 and 24 volts]]

External power adapters can fail, or can become separated from the product they are intended to power. Consequently, there is a market for replacement adapters. The replacement must match input and output voltages, match or exceed current capability, and be fitted with a matching connector. Many electrical products are poorly labeled with information concerning the power supply they require, so it is prudent to record the specifications of the original power supply in advance, to ease replacement if the original is later lost. Careful labeling of power adapters can also reduce the likelihood of a mixup which could cause equipment damage.

Some "universal" replacement power supplies allow output voltage and polarity to be switched to match a range of equipment.<ref>[http://computertimes.com/may06edchoiceiGoeverywhere130.htm Computer Times: 2006 review of a satisfactory third-party universal AC adapter] {{webarchive|url=https://web.archive.org/web/20141013005435/http://computertimes.com/may06edchoiceiGoeverywhere130.htm |date=2014-10-13 }}</ref> With the advent of switch-mode supplies, adapters which can work with any voltage from 110&nbsp;VAC to 240&nbsp;VAC became widely available; previously either 100–120&nbsp;VAC or 200–240&nbsp;VAC versions were used. Adapters which can also be used with motor vehicle and aircraft power ''(see [[EmPower (aircraft power adapter)|EmPower]])'' are available.<ref>{{cite web |url=http://www.tomshardware.com/reviews/laptop-universal-power-adapter,2852.html |work=Tom's Hardware |title=Universal Laptop Power Adapters For The Air, Road, And Wall |date=September 2, 2011 |author=Andrew Ku}}</ref>

Four-way '''X connectors''' or six-way '''star connectors''', also known as '''spider connectors''', with multiple plug sizes and types are common on generic power supplies. Other replacement power supplies have arrangements for changing the power connector, with four to nine different alternatives available when purchased in a set. This allows many different configurations of AC adapters to be put together, without requiring soldering. Philmore and other competing brands offer similar AC adapters with interchangeable connectors.

The label on a power supply may not be a reliable guide to the actual voltage it supplies under varying conditions. Many low-cost power supplies are "[[Voltage regulator|unregulated]]", in that their voltage can change considerably with load. If they are lightly loaded, they may put out much more than the nominal "name plate" voltage, which could damage the load. If they are heavily loaded, the output voltage may [[Voltage droop|droop]] appreciably, in some cases well below the nominal label voltage even within the nominal rated current, causing the equipment being supplied to malfunction or be damaged. Supplies with linear (as against switched) regulators are heavy, bulky, and expensive.

Modern [[switched-mode power supply|switched-mode power supplies]] (SMPSs) are smaller, lighter, and more efficient. They put out a much more constant voltage than unregulated supplies as the input voltage and the load current vary. When introduced, their prices were high, but by the early 21st century the prices of switch-mode components had dropped to a degree which allowed even cheap supplies to use this technology, saving the cost of a larger and heavier mains-frequency transformer.

===Auto-sensing adapters===
Some universal adapters automatically set their output voltage and maximum current according to which of a range of interchangeable tips is fitted; tips are available to fit and supply appropriate power to many notebook computers and mobile devices. Different tips may use the same connector, but automatically supply different power; it is essential to use the right tip for the apparatus being powered, but no switch needs to be set correctly by the user. The advent of switch-mode power supplies has allowed adapters to work from any AC mains supply from 100 to 240 V with an appropriate plug; operation from standard 12 V&nbsp;DC vehicle and aircraft supplies can also be supported. With the appropriate adapter, accessories, and tips, a variety of equipment can be powered from almost any source of power.

A "Green Plug" system has been proposed, based on [[Universal Serial Bus|USB]] technology, by which the consuming device would tell the external power supply what kind of power is needed.<ref>[https://www.engadget.com/2008/05/10/swtched-on-green-plug-tries-to-replace-the-worry-warts-part-1/ Green Plug tries to replace the worry warts] Engadget May 2008</ref>

=== Battery eliminator ===
[[File:Roger's Batteryless Ad.jpg|thumb|November 1925 magazine ad for battery eliminator]]
A battery eliminator is an adapter intended to allow a device intended for battery operation, such as a radio, to be operated from an AC outlet.<ref>{{Cite web |title=What Google is buying: Motorola's 83-year history of invention |url=https://money.cnn.com/galleries/2011/technology/1108/gallery.motorola_history/index.html |access-date=2023-06-25 |website=CNNMoney}}</ref>

All radios, except [[crystal set]]s, used inconvenient and messy [[vacuum tube batteries]] until the mid- to late-1920s. Battery eliminators that plugged into [[light socket]]s became very popular.<ref name="ramirez1993">{{Cite book |last=Ramirez |first=Ron |url=https://www.worldradiohistory.com/BOOKSHELF-ARH/History/Philco-Radio-1928-1942-Ramirez-1993.pdf |title=Philco Radio 1928-1942 |publisher=Schiffer Publishing |year=1993 |isbn=0-88740-547-9 |location=Atglen, Pennsylvania |pages=6–7, 10 |access-date=2024-12-13}}</ref> Early commercial units were produced by the [[Edward S. Rogers, Sr.]] company in 1925 as a complement to its line of [[batteryless radio]]s.<ref>{{Cite web |title=Rogers Recollections: A Chronicle of Excellence and Achievement |url=https://ewh.ieee.org/reg/7/millennium/alternating_current/ac_recollections.html |access-date=2023-06-25 |website=[[IEEE]]}}</ref> Another early producer of battery eliminators was the Galvin Manufacturing Corporation (later known as [[Motorola]]), which was opened on September 25, 1928 by [[Paul Galvin (businessman)|Paul Galvin]] and his brother Joseph E. Galvin.<ref>{{Cite web |title=Work begins at company that designs first mass-produced car radios |url=https://www.history.com/this-day-in-history/first-day-of-work-at-the-galvin-manufacturing-corporation |access-date=2023-06-25 |website=HISTORY |language=en}}</ref> Eliminators became obsolete for radios after [[RCA]] introduced [[Vacuum tube#AC power|AC tube]]s in 1927, enabling receivers to plug into [[household power]]. The industry rapidly adopted AC tubes, and companies which launched exclusively manufacture that product such as [[Philco]] had to quickly pivot to radio manufacturing to remain relevant and existent. {{r|ramirez1993}}

===Laptop charger===
In early [[laptop]] computers, the [[power supply unit]]s were internal like in [[desktop computer]]s. To facilitate portability by sparing physical space and reducing the weight, power supply units were externalized.<ref>{{cite web |url=https://www.pcworld.idg.com.au/slideshow/353969/gallery-25-years-toshiba-laptops/|title=Gallery: 25 years of Toshiba laptops }}</ref>

When a laptop computer is operated while recharging, the [[integrated circuit]]ry which controls the charging makes use of a power supply unit's remaining [[electrical current]] capacity. This allows supplying the device's components with power during usage while maintaining an uncompromised constant charging speed.