I have a Dell Dimension 9200 myself.
Love it, flexible, upgradeable, inexpensive & very capable PCs.
Dell sold the Dimension 9200 from new with the option for a 8800GTX card so the PSU is perfectly capable of handling that card.
My own one runs a Q6700 quad Intel CPU, 4gb of RAM (2 x 2gb sticks), an Nvidia 9800GT graphics card, 2 x 1tb Western Digital HDDs, 2 x DVD burners, a Soundblaster Audigy SE card, a floppy drive unit & a card reader.
All on that standard 375wt Dell PSU.
The thing about Dell PSUs is that they measure the output honestly.
Lots of other manufacturers have a habit of quoting a briefly held peak output as if it is the rock solid dependable sustained 100% maximum.
It often is not.
Briefly held peaks just exaggerate the specs for the spec-sheet number obsessed.
So graphics card makers, so as not to end up with loads of angry ex-customers, usually tend to err on the side of caution and quote required specs & numbers which make the Dell look as if it doesn't stand a chance of meeting.
But they often do.
I reckon my own is pretty much maxed out & I want to dump the floppy unit which I never use & replace it with another 1tb HDD & I'd like a much more up to date graphics card (the Nvidia 460GTX looks great value right now).
My solution?
Another Dell PSU.
750wt this time.
It'll keep me going for quite a while yet I reckon.
Your original card could have failed for any number of reasons but a weak PSU is not the most likely cause
(you'd get all sorts of obvious PSU-related problems before that - things like sudden & repeatedly rebooting being the obvious symptom & parts of your rig operating but not others, fans slow or failing to operate).
I'd just add that you haven't mentioned the rest of your spec but I guess if things were added that were not initial standard fit & your PC was running a couple of hard drives & a high spec CPU it might be pushing things but I'd certainly expect the usual PSU problems to be apparent than just having things work normally and then experiencing a graphics failure after 3yrs.