old style eca stack did work, since they actually stimulated the beta 3 (or 6, can't recall) androrecpetors in the body to actually increase your bodies metabolic state. It did so by raising burn by increasing blood pressure and heart rate. side effects include heart attack and stroke. Something fat people are already at elevated risk of, hence the ephedrine ban.
current generation of fat loss pills are 100% complete and utter waste of money. This is straight up fact, every single pill on the market for non prescription use is completely fake. they do nothing. There is not a single peer reviewed double blind study out there that is able to produce any fat loss results better than plecebo in any trial.
Long story short, save your money.