Dc USB plug:

This USB PLUG, plug is compatible with 13.8 and 28 volt aircraft and is compatible with existing or new cigarette lighter receptacle, LS03-05025 (POWER ADAPTER) which may be installed in the aircraft.  The USB plug is a new design built to survive ruggedized airborne conditions and is qualified by  DO160G testing.    

Caution:

Overseas USB plugs fail to meet any quality standards for even commercial mobile applications.  During our testing the majority had severe over temperature, over current and circuit deficiencies.  Smoke in the cockpit and other short circuit conditions have surfaced during the last couple of years as the ipad cockpit applications have grown in popularity.