Right now those people get food stamps and welfare

Wow, talk about living in a bubble. Do you really think that a person who runs out of money can just go and get more from the government?

My sister gets food stamps. Food stamps are for food (generally) where as money is for anything. UBI is often held up by proponents as a replacement for all other support. Given them $1k a month cash instead of whatever they get now. But what they get now is trying to solve a problem not solved by UBI, namely that they can't be responsible for themselves (for whatever reason, physically unable, mentally unable, kids, etc...) UBI doesn't fix that problem so the existing programs will still need to exist.

Anyone unable to be responsible can receive their UBI via a cashless welfare card (https://en.wikipedia.org/wiki/Cashless_Welfare_Card) which quarantines where the money can be spent. It deals with issues like problem gamblers and people with substance abuse problems.

hahahah what? Those are directly based on salary, not on "salary after you spend most of it". How would you even implement a system like that?

You'd dole out UBI biweekly or whatever to solve the same problems that food stamps solve? I agree it's a good question though.