The advent of switch-mode power supplies has allowed adapters to work from any AC mains supply from 100 to 240V with an appropriate plug; operation from standard 12V DC vehicle and aircraft supplies can also be supported. This interval is measured in cycles per second, or hertz (abbreviated Hz). An AC adaptor is used to convert one AC voltage into another AC voltage. The label on a power supply may not be a reliable guide to the actual voltage it supplies under varying conditions. The internal circuitry of an external power supply is very similar to the design that would be used for a built-in or internal supply. Archived from the original on 15 July 2011. Retrieved 2011-06-03. ^ Adams, Douglas. «Dongly things». . This is particularly relevant for equipment with lightweight cases which may break and expose internal electrical parts.
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. The ITU recommendation was expanded and updated in June, 2011. The hope is to markedly reduce the profusion of non-interchangeable power adapters. Adapters for battery-powered equipment may be described as chargers or rechargers (see also battery charger). AC adapters are used with electrical devices that require power but do not contain internal components to derive the required voltage and power from mains power. Ease of replacement – Power supplies are more prone to failure than other circuitry due to their exposure to power spikes and their internal generation of waste heat. Retrieved 2011-06-03. ^ Alter, Lloyd. «Google Pushes for PC Electrical Efficiency; Side Effect: No More Wall-Warts». . Careful labeling of power adapters can also reduce the likelihood of a mixup which could cause equipment damage.
Other replacement power supplies have arrangements for changing the power connector, with four to nine different alternatives available when purchased in a set. Due to the nature of its constantly-reversing electrical current, AC electricity can damage some electrical circuits that were designed for DC electricity. Mains voltage is rectified to a high direct voltage driving a switching circuit, which contains a transformer operating at a high frequency and outputs direct current at the desired voltage. For example, a 12 V DC adaptor sold in the United States will convert 120 V AC at 60 Hz into 12 V DC.Like its AC counterpart, a DC adaptor is also rated for maximum power output in watts. When purchasing a power adaptor for your electrical device, there are two general types: AC adaptors and DC adaptors.