AC adapter

Safety can be another advantage, as hazardous 120 or 240 volt mains power is transformed to a lower, safer voltage at the wall outlet before going into the appliance handled by the user.

Originally, most AC/DC adapters were linear power supplies, containing a transformer to convert the mains electricity voltage to a lower voltage, a rectifier to convert it to pulsating DC, and a filter to smooth the pulsating waveform to DC, with residual ripple variations small enough to leave the powered device unaffected.

Losses in the transformer and the linear regulator were considerable; efficiency was relatively low, and significant power dissipated as heat even when not driving a load.

A linear circuit must be designed for a specific, narrow range of input voltages (e.g., 220–240 VAC) and must use a transformer appropriate for the frequency (usually 50 or 60 Hz), but a switched-mode supply can work efficiently over a very wide range of voltages and frequencies; a single 100–240 VAC unit will handle almost any mains supply in the world.

Many inexpensive switched-mode AC adapters do not implement adequate filtering and/or shielding for electromagnetic interference that they generate.

Even WiFi reception in the gigahertz range can be degraded if the receiving antennae are very close to a radiating AC adapter.

The advantages include: A survey of consumers showed widespread dissatisfaction with the cost, inconvenience, and wastefulness of the profusion of power adapters used by electronic devices.

[3] The issue of inefficiency of some power supplies has become well known, with U.S. president George W. Bush referring in 2001 to such devices as "Energy Vampires".

In 2002 most external plug-in "wall wart" power adapters commonly used for low-power consumer electronics devices were of linear design, as well as supplies built into some equipment.

The website where the report was published said in 2010 that despite the spread of SMPSs, "today's power supplies consume at least 2% of all U.S. electricity production.

Some "universal" replacement power supplies allow output voltage and polarity to be switched to match a range of equipment.

[11] Early commercial units were produced by the Edward S. Rogers, Sr. company in 1925 as a complement to its line of batteryless radios.

[13] Eliminators became obsolete for radios after RCA introduced AC tubes in 1927, enabling receivers to plug into household power.

To facilitate portability by sparing physical space and reducing the weight, power supply units were externalized.

[14] When a laptop computer is operated while recharging, the integrated circuitry 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.

The USB connector (and voltage) has emerged as a de facto standard in low-power AC adapters for many portable devices.

[15] Electric fans, lamps, alarms, coffee warmers, battery chargers, and even toys have been designed to tap power from a USB connector.

Conformant supplies deliver 5 VDC via a micro-USB connector, with preferred input voltage handled ranging from 90 to 264 VAC.