The proliferation of portable and laptop computers has greatly expanded the need for consistent, reliable power sources. Many battery-powered electronic devices can be operated using an alternating current (AC) source converted to a direct current (DC) voltage by way of a suitable power adapter. Portable electronic devices such as notebook or laptop computers, hand-held computers or personal digital assistants, digital cameras, portable CD-RW drives, and cellular telephones may be operated from a DC power source such as a rechargeable battery or an AC-to-DC adapter. Since the life of a rechargeable battery is limited, an adapter is usually one of the accessories transported along with a portable electronic device. In many of these designs, the output voltage from the power adapter is used to not only power the electronic device, but also to recharge batteries. In fact, many devices today allow for fast recharging of batteries even while the device is operating.

A portable electrical device is often powered by an internal power source, such as a battery pack. The internal power source which is usually a rechargeable battery set requires recharging. Thus, a power adapter is used to connect the portable electrical device to an electrical main, such as a wall outlet, for recharging the internal power source or directly powering the portable electrical device. A power transformer (AC adapter) is widely used for supplying power to portable electronic devices and/or for recharging batteries of such electronic devices. The power transformer includes a housing, a plug protruding from the housing, a conversion circuit provided inside the housing and an output cord extending from the housing. In order to plug the power adapter to the power socket, the pins are inserted into the power socket. In the converting circuit, an alternating current supplied from the power socket is converted to a direct current of a predetermined voltage. The obtained direct current is output from the output cord which may be connected to an electronic device.

A power adapter generally comprises an insulating casing and a power transforming device disposed in the insulating casing. The power transforming device generally comprises a transformer and a PFC (power factor correction) choke. AC adapters generally include a plug which plugs into a wall outlet, a transformer which steps the line voltage down, a rectifier circuit which rectifies the stepped-down AC voltage to a DC voltage, and a plug which plugs into an electronic device. Generally, power adapter devices comprise an adapter body, a primary-power input cable for coupling to a commercial AC power supply and a secondary-power output cable for coupling to a desired load or external equipment. Among such known power-supply adapter devices is one where the primary-power input cable is detachably coupled to the adapter body with the secondary-power output cable integrally fixed to the adapter body. Power adapters generally include only one connection for an outlet fed with electric energy from the outlet of the power supply and allowing attachment of electronics devices. Portable electronics devices have a port for connecting to the adapter, and the port has a plurality of contacts disposed therein. Power adapters are generally provided with a pair of cords extending from a structure in which electrical circuitry for converting power input through one of the cords to a desired power level to be output through the other one of the cords to an electrical device.

A power adapter receives a commercially available alternating-current (AC) power and convert the AC power into a direct-current (DC) power in order to enable a DC/DC converter to transform a high-level DC voltage into various low-level DC voltages. An alternating current (AC) adapter is also known as a power transformer. AC adapters are used for various purposes such as the recharging of mobile phones and the converting of AC voltage into a desired AC voltage or a DC voltage. Alternating current adapters transform voltage from a high level (e.g., 120V) to a lower, usable level (e.g., 3V, 6V, 12V, 24V). These adapters convert alternating current into direct current (DC). Most electronic devices are designed to operate using a direct current (DC) voltage source. The transformation of a high voltage AC signal to a lower voltage DC signal allows these devices to use power from standard wall outlets. AC adapters generally include a transformer to reduce the voltage level and a rectifier to convert AC signals to DC signals. A regular switching type AC adapter for an electric apparatus is comprised of a switching element, which is alternatively switched on and off to let a stable voltage be provided to the electric apparatus for working.

Since AC voltage supplies in various countries, the input of the power transforming device is interchangeable to fit different AC voltages, such as 110V and 220V. Generally, the electrical adapter electrically interconnecting with different interface standard connectors performs the functions of signal/power transmission and conversion therebetween by two ways. If the numbers of electrical contacts of the different interface connector are equal, the adapter may mechanically and electrically connect corresponding contacts directly. In the other hand, the adapter need comprise a printed circuit board thereof which can perform the functions of signal/power transmission and conversion if the numbers of the different standard connectors are different. Generally, a power adapter is always used for adapting different sockets provided in different countries when traveling all over the world.

Numerous types of adapters have been developed, each having a rated voltage for a particular device and each having a plug which has a particular configuration engageable with a compatible socket of that particular device. Adapters currently on the market include power adapters and data adapters which each have a plug for connecting to a portable device, but the plugs differ in the location and number of the contacts used in the plug. Power adapters are used to charge the portable device; data adapters are used to exchange the data with a PC. Universal serial bus (USB) interfaces are widely used on PCs today. Standard USB ports also include power terminals for providing power and data through a USB interface between a portable device and a PC so that the PC can transmit power to the portable device while the portable device and the PC exchange data.