UPDATE: see http://www.thingiverse.com/thing:756963 for enhanced plug with new features. The customizer stays at the same link that's posted here.

This is a plug that can be customized to your need.
All STLs attached here are created from the same customizer.

If you need a plug in a particular size, and want to adapt the shape of the cap or the bottom, there are many options in the customizer.

Navigate to
http://beta.gigmade.com/2015/03/universal-plug/
and customize with your own parameters.
Download STL.