AC Adapter - Problems

Problems

While useful for many purposes, some external AC adapters have attracted criticism. Problems with this type of power supply include, but are not limited to:

1. Size — Power supplies which plug into the mains directly without using a plug on a cable (true wall warts) are bulkier than bare plugs; sometimes they are too large to plug into power sockets with restricted space, or into adjacent sockets on power strips.
2. Weight — Some AC adapters can be heavy, exerting excess weight on the power socket (this depends on the socket design of the country in question). Some external power supplies are "power bricks" (also known as "line lumps") having a short AC cord so they can lie on the floor, thus relieving strain, at the expense of clutter. Other wall-hanging types are made long and thin, minimizing the leverage of their weight vector that pulls the plug out, at the expense of exacerbating the size problem. The weight for equipment that must be carried (e.g., for traveling) is not a disadvantage of external supplies, as the alternative is an equally heavy internal supply; in many cases a single universal supply can replace several proprietary ones.
3. Inefficiency — Some idling power is wasted as the power supply is left running when the equipment power switch is off or the equipment is disconnected from the power supply. In recent years it has become common for equipment with internal supplies to share this problem due to the use of a "soft" power switch.
4. Confusion — External power supplies are often generic and not clearly marked to identify the equipment they are designed to power. It is very easy to separate power supply and equipment, and difficult to re-match the many power supplies and devices that users possess. USB and cigarette lighter receptacles are examples of better understood standards that don't confuse users as much, though one might think that the receptacles are only compatible with automobiles when their useful compatibility encompasses almost anywhere with a 12 volt DC power source.
5. Compatibility problems — There is no standardization of connectors; the same connector is often used for different voltages, and for both DC supplies and AC-to-AC transformers. This easily leads to using the wrong power supply, which can destroy equipment. However, USB is always used for 5 volt output, and cigarette lighter receptacles are almost always used for 12 volt to 24 volt output (tip positive, sleeve negative).

Disadvantages 3, 4, and 5 are also applicable to some 12 volt DC adaptors made for cigarette lighter receptacle use in automobiles, or connections to a plain 12 volt lead-acid battery.

A survey of consumers showed widespread dissatisfaction with the cost, inconvenience, and wastefulness of the profusion of power adapters used by electronic devices. The science fiction author and satirist Douglas Adams once wrote an essay bemoaning the profusion and confusion of power adapters, and calling for more standardization.