yeah, the original power supply has a weird molex type connector that supplies power to some fans and junk in there. it's quite common to hack them off and scab them onto a new supply since it's non-standard.
the power supply should have a bracket that holds it down, yes. it's not required... some double sided tape under it could keep things in place sufficiently.
I can take a pic of the bracket when i get home if you like... I have a couple for parts in my basement right now. you might be able to cobble something up to work.