It's the mini tower..sorry for not answering your question sooner.
EDIT: Oh yeah and the mini tower is the largest size...in descending order it's the mini tower, desktop, small form factor, and ultra small form factor.
Sorry bad news. The motherboard power socket is a custome design. Only that dell psu is gonna fit it and fit in the case. Man I truely wished you had come to us first. You could cancle the order or just return it. Something to think about.
Sorry I couldn't help you any farther.
Wow...that sucks...so you think there's a possibility that there are any generic psus out there that'll fit into it? Well in any case...thanks for trying