99% of all fat burners main ingredient is 200mg Caffeine(the FDA approved amount)
thats whats reducing your appetite, the other stuff is extra
you can buy 80 caplets of caffeine for 5 bucks from walmart/walgreens(buy one get one free if you catch it on sale)
b-complex can run you anywhere from 5-8 bucks(also commonly buy one get one free)
the difference with EC stack is its the same 200mg caffeine but ephedrine acts as a catalyst and increases the amount of noradrenaline in your system than would caffeine alone(by an appreciable amount) this also in turn increases your heart rate(and for some in the past who have taken more than the necessary dosage, can result in a heart attack

)
the reasoning for the dosage is:
1) ephedrine and caffeine both have half-lives of roughly 3-6 hours, meaning they havent broken down and can be used for the their intended effect
2)taking more caffeine than that + the ephedrine can result in heart palpitations
its because of ephedrine making caffeine overly potent is why it was taken off the market for fat burners.
but if your intent is appetite suppression nothing does it like EC stack

the A is for asipirin which dilates your blood vessels and reduces blood pressure, fishoil is safer imo if you are dosing correctly
but yes, damn near all fat burners have the same concoction of 200mg caffeine plus other ****. B-vitamins improve your bodies ability to metabolize food(by how much is unknown) so in theory, the two together give you a nice stimulant for workouts
taking from this, it would be wise to always consume with food for best results