I might have got 2 bad Ernst jacks... but I could not plug into it without reducing the width, etc. of the male plug going into it.
I also have a plane with a GP change jack. It did the same thing...... pushed out the back.
I now buy nothing but MPI chanrge jacks. They are about $15 at my LHS and worth every dollar!!!
They have a new one now that has LED's that is a built in volt watch. It is a hefty $25.
Here is the site for the $25 model..... the $15 model looks the same, just no LED's.

http://www.maxxprod.com/mpi/mpi-4.html#LED Charge Switch

This site is a pain loading, at least with my dial up. .............. lownslo....