Powwow culture really began in the 1940's and 50's and (because it is a social event, and often inter-tribal) it developed it's own culture and fashions and dance styles, mostly taken from plains cultures. There are regional variations in regalia, though they are probably too subtle for an outsider to notice. So, in a way you are correct, in that powwow regalia is kinda it's own thing, and itsn't much related to a tribe's ceremonial regalia, because powwows again are public social events, while ceremony is a private spiritual event,
As for moccasins..every tribe had it's own style of footwear, even if people did sometimes go barefoot in the summer for a period of time ( as happens everywhere, in every culture. I can find photos of victorian british people barefoot...that doesn't mean they didn't wear shoes on a regular basis)
Moccasin styles are unique to each tribe, btw. I'm sure if you google it, you can see examples of the hundreds of different types. (also, in my tribe, men and women wear a different style. Our women's mocs have a white wrap that goes up to the knee, kinda like a gaitor) and our mocs have very thick hard soles. ( important when you live in the desert with hot sand, sharp rocks, thorns, and snakes)
Here's what our mocs look like:
Hope that's helpful. If you need more detail, you can email me through YA.