What PSU's can fit in this case?

Solution
Newer Dells USE EPS12V 2.92 power supplies not ATX. The default in the mini tower is 949H1.

CX Series from Corsair is not recommended.

TX HX CS Series is fine.
Newer Dells USE EPS12V 2.92 power supplies not ATX. The default in the mini tower is 949H1.

CX Series from Corsair is not recommended.

TX HX CS Series is fine.
 
Solution