I don't know why but more times than not with these OEM systems they never list the PSU that it comes with.
However I do know sometimes with Slimline cases and OEMs they don't use a standard sized PSU which makes it difficult to upgrade things thus causing you to be more prone when the time comes to purchase a new system from them.
If it were me I would either call Fry's or if one was nearby check to see that a standard PSU will fit.
As for the Graphics card, Once again seeing and measuring the inside of the case would help determine what card would fit as some of the newer cards are very long and require dual slots.
If you were able to find out if you can easily upgrade your power supply then I know XFX makes a 5 series card that is a single slot card.
And as for the power supply any Branded quality 80% efficiency that meets or exceeds the new cards minimum wattage (actually voltage on the 12V rail)(s) with the proper 6 pin connectors would be fine.
Fabe