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A DC jack is a component used in many electronic devices that allows a steady power source to be plugged in. Though electronics require direct current (DC) power, alternating current (AC) is the type of electricity supplied to and available in household wall sockets, mainly because of its ability to be delivered over long distances without losing strength. Therefore with most electronics, an AC adapter connected to a DC jack is necessary to supply power in a usable way.
Unlike AC plugs, which are uniform and regulated on a country-by-country basis, DC jacks and plugs, which are technically referred to as coaxial power connectors, are generally not standardized. Many electronics manufacturers have their own proprietary AC adapters, also known as power bricks, which employ unique sizes of DC jacks. Currently Germany and Japan are the only countries that have attempted to issue standards for DC jack sizes. Different AC adapters and DC jacks can vary in many ways, ranging from voltage to physical diameter.
Given the fragile nature of electronic circuitry, power supplies from different devices should not be mixed and matched. A DC jack is designed to accept only one size of connector. While various sizes may indeed look similar, it can be potentially dangerous to try and pair an unsuitable power supply with a device.
While the most common DC jack connectors measure .21 inches (5.5mm) in diameter and .37 inches (9.5mm) in length, it is not unusual to encounter some that are much longer and wider. Though not an absolute rule, larger connectors typically indicate higher voltages. Sony® is notable for instituting a system for its devices that indicates voltage in this way.
With laptop computers in particular, a DC jack is susceptible to suffering from wear and tear over time. With frequent connections and disconnections, the jack itself can begin to loosen and wear down it its housing, allowing the connector to slip out and disrupt power. While do-it-yourself repair can restore a tight fit without expensive labor costs, soldering is required and, for amateurs, the risk of doing greater damage to the device can be considerable.
Less common than the DC jacks that pair with AC adapters are styles known as snap and lock connectors. These jacks are standardized, with an outer diameter of .394 inches (10 mm) and connecting pins of .06 inches (1.5 mm) in diameter. The outer jacket of a snap and lock connector is grooved in such a way that matches grooves inside the paired DC jack, offering a resilient physical connection. Examples of this design include the PS/2 connections used by some computer keyboards and mice.