Is Dell power supplies good?

Yeah, it can really depend. I have had to change the power supplies on all the Dells I have owned. The power supplies really feel like they were made just to make the computer run.
 
Dell makes good power supplies.

The problem is the xps 630 is pretty old from around 2008? If you have had it for a while, it might be worth it to get a new PSU although if yours is from like 2010, then I'd still use it.

PS: The case is awesome looking and I know of people who have kept the case and rebuilt using the dell case.
 



You have a point but there is a saying, "If It Ain't Broken, Don't Fix It"