I was away from crypto for years and now I'm trying to get back into the game. I was really STUNNED that there is no exchange, even after many years since bitcoin started, that we can just deposit USD and start exchanging altcoins. I hope I'm wrong because this would be the single biggest hurdle for altcoins to be widely adopted by general public. There are just too many hurdles to jump over just to START trading.
If you are looking an exchange that allows to deposit USD to buy crypto currency you can try to use quoinex this is a crypto-fiat exchange. I have no past transaction on this but on its other service exchange qryptos crypto-crypto offers the best service and this makes me confident that quoinex exchange as the other version has the same performance as well. You can try for yourself.