whats the "power port" door/plug for on one of them hand held programmers???

 

I have seen a supercharger program that plugs into it. More info in my old posts.

 

The HPP programmers for the OBD-II cars had a port in the bottom that could be used to load a "custom" tune (a module, provided by Hypertech) or to insert a cartridge that allowed the HPP to be used as a scanner.