From my observations, they are two completely different animals.
XForce makes me feel as if I have the physical energy of an ECA stack, but with great mental focus and almost no undesirable side effects like jitters.
Adrenaline, even dosing 4 caps at once, never really makes me feel physically stimulated, just a little bit, but the mental clarity is awesome.
Heck, I may just stack the two tomorrow night and let you know what I experience!