Here is the difference in the power supplies.http://www.tomshardware.com/2004/12/23/more_performance/page2.html
-->Are you using the 6 pin adapter supplied with the video card or did you use the power supplies 6 pin adapter?
You shouldnt have done any damage by plugging it in
It sounds to me like the PSU, the older power supply maybee starting up part of the system but with out the extra 12+ V power it may not start. Depends on how it was designed.
I would try and RMA the PSU unless someone else has any input.