US Patent 7632137 Power adapter

A power adapter has a main body of cylindrical shape. A top of the main body defines a recess and an annular sidewall enclosing the recess. A rotation-proof component received in the annular sidewall of the main body defines a rotation-proof portion extending into the recess. A plug is rotatably mounted in the recess, and a side of the plug defines at least one rotation-proof recess. The plug is rotatably secured in the recess then the rotation-proof portion is elastically pressed against the plug and finally the rotation-proof portion is released into the rotation-proof recess for restraining the plug from reverse rotation.