Mixing various contact enhancer?? Craig/Walker/VDH

There are quite a few contact enhancers available from different companies. eg: VDH, Craig, Walker, Xtreme Quick Silver.

If I have applied on product already and like to try the product from another comapny, do I need to clean off the contact surface first by some special chemical???

Or a combination of different product will yeild better or negative effect? I guess you can never clean the stuff out that is left inside an AC outlet, so they are mixed at that contact point anyway, right?

Thanks for your input.
Try the Caig de-ox-it D5.It should remove the various contact-enhacers.It works with Lloyds' SST/E-SST.