Each type of supplement comes at a range of prices. There's the cheapo which no one expects to work and few people buy; it's there so you feel good about the higher priced item your about to purchase. Then there are a handful of mid priced supplements. These are the ones people actually buy. They are also tiered so the store can capture the price point of the varied economic classes of its patrons. Finally, come the ridiculously over priced uber strength supplements. They have price tags starting around $80 and heading into the hundreds. Only fanatics and the most gullible dupes actually purchase these. Their main purpose is to make you feel like the money you blew on gelatin, starch and lactose was well spent.
Read Amazon reviews. It's pretty amazing what people can come up with.
I take the usual suspects: Magnesium (I run almost every day) and a Omega 3/Vitamin D combo (I don't eat fish and we don't get a lot of sun here in northern Germany). Seems like a reasonable thing to be doing but I can't for the life of me tell any difference with or without them. I do buy the cheap ones though - maybe I'd feel 10 years younger if I'd buy the top shelf ones...
Then you have the dietary macronutrient supplements (Protein, Omega 3, etc), the multivitamins and the specific functional foods.
Your "good diet" is probably lacking some micronutrients (some websites or fitness trackers allow you to set your diet and they will show exactly what's missing related to the guidelines) so I'd rather go with multivitamins (or at least Vit D)
I wondered how do people by this stuff believing it helps them (as opposed to the usual remedy of sleep, exercise, and good diet). Than I asked my self, maybe I'm missing something! Should I be taking supplements too?