Ecstacy is a pill form of MDMA and should not contain extras. It could have MDEA and MDA instead of MDMA, which are very similar. It mostly depends on the chemicals these factories are able to get. The fact that junk pills do contain other stuff like caffeine, doesnt make Ecstacy normally a mix. There are mix pills which contain amphetamine, 2CB or LSD but these are sold under their own, different name.
I don't know if you've ever seen a pill factory from the inside, but I have here in the Netherlands. Also I've seen loads of ecstacy tests, as we are free to test our drugs here.