Now you are about to get analysis paralysis. It's knocking at your door. Don't let it get in.
USB scopes are recommended only when you can't afford an entry-level 4 channel benchtop scope or have some special portability needs. If that's the case, it seems most people think Owon VDS1022 is the worthiest one. There's no point purchasing a "more capable" USB scope if a cheaper one can do what you need it to do. The "more capable" one will remain always an USB device and it will always have the shortcomings of an USB scope.
Please note I am lucky enough to have one of these benchtop 4 channel scopes in the $500 range, so I don't have any user experience with USB scopes. I think Owon VDS 1022 could do all you need it to do, but you'll have to check it yourself.
Now, to make your decision, there are some pointers:
Dave's video explains, much better than most of us could ever do, what you need to measure PSU ripple/noise. Do you think VDS1022 is able to do what Dave says in that video? Check the specs. Has it enough bandwidth? Enough channels? Enough sensitivity?
Go to Gyro's thread. Is people happy with Owon VDS1022? What do they say about how it works? How do they compare it with other USB devices? You should search the forum for threads about the different candidates. Only you know what device you can really afford.
If you read Gyro's thread, you'll find there is people who purchased the non-isolated version and converted it to the isolated version afterwards. It doesn't seem to save much money, but if your budget is so tight, it could allow you to make your initial expense lower while retaining the ability to upgrade in the future. Many purchased the non-isolated version, seem to be happy with it, and do not feel any need to upgrade to the isolated version.
You'll find also that many owners of Owon VDS1022 are using an unofficial software which seems to solve some shortcomings the official one has, see
https://github.com/florentbr/OWON-VDS1022Owon VDS1022 is Dave's recommendation if you have to put together an electronics lab for just $300 in all. See:
See what Dave says about USB scopes when you don't have to squeeze your wallet so much (go to 3:06 if you want but the whole video is worth watching):
You just need some hours of reading posts and to watch some videos, not just about VDS1022, but also about any other device you could be interested in. I think you have now enough pointers to do an informed decision, which can only be made by you.
It would be a little bit bizarre if, being you the prospective buyer, would be also you who doesn't read the relevant threads nor watch the dedicated videos, don't you think so?