Connector Construction and Terminology
Some power plugs are merely miniaturized TRS connectors ("phone plugs" in North America, "jack plugs" in the UK) which have been pressed into service as power connectors. The two connectors on the left of the picture above are subminiature and miniature plugs respectively, the subminiature size being 3/32 inch (or 2.5 mm), and the miniature being 1/8 inch (or 3.5 mm) in diameter (the original full-sized plug was 1/4 inch in diameter). The original application of these connectors was for audio microphones, headphones and headsets. Phone/jack plug connectors were not originally designed to carry power, and there is a possibility of momentary or continuous short circuiting the power supply when mating the connector.
By contrast, coaxial power connectors were specifically designed to carry electrical power, and usually have features intended to make connections safer and more reliable. Typically, the outer body of the plug is one metallic contact, most often but not always connected to the negative side of the power supply. Coaxial power connectors generally have a cylindrical hollow insulated tip constructed to accept insertion of a pin (note that exceptions are described later). A pin mounted in the corresponding socket connects with this second contact, which is an internal metallic surface lining the inside of the tip of the plug.
The outer plug contact is usually called the barrel or sleeve, and the inner contact is called the tip (by analogy to the same terms used for phone/jack plugs), although in the case of most coaxial power connectors the very end of the tip itself is a non-conductive ring.
Technically, most coaxial power plugs are considered to be of "female" gender, and most coaxial power jacks are considered to be "male". For a more detailed discussion of this naming convention, see the article on gender of connectors and fasteners. As a notable exception, some special-purpose coaxial power connectors typically used for higher power levels are male gender, e.g. the larger size EIAJ plugs.
In a typical coaxial power configuration, the mating jacks or sockets have a somewhat oversized circular opening with a pin in the center. There is typically a single spring-loaded contact at the side of the opening, so some variation in mating plug barrel diameters can be accommodated. If the central pin of the jack is too large for the opening in the plug tip, it is not possible to make the connection. The pin should be designed to be just slightly smaller than the hole, to make a reliable connection. If the pin is substantially smaller, the connection may appear to work but may also be somewhat loose and unreliable.
Most coaxial power connectors are not sealed against entry of water or dust, but at least one manufacturer (Switchcraft) has announced a series of water-resistant coaxial power plugs and jacks.
Read more about this topic: Coaxial Power Connector
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