I have a bad 250 watt power supply in a dell dimension 4600. Can I replace it with a 350 watt PS?

I'm not positive on that one, but bet someone will come along who knows for sure.

I pipe in because the PS went out on my computer last year and I found that a case with PS was cheaper than the PS alone - and I liked the case a lot better to boot.

I went the new case w/PS route and was glad I did.

Watts of the power supply does not matter for which mechine. It only matters if you try to connect to many drivers. The more drivers you have the more power you will need. Since 250w works for your PC, any PS will do.

Guest probably meant drives NOT drivers... and you can swap out the old for a new just take it to a local computer vendor and match up the size of the power supply... some could be physically larger and smaller than your but should be no problem... good luck