eatmypie :
Dellmakes fairly good power supplies so I wouldn't worry about that part, I would almost recommend something like a gtx 550 since I'm guessing you are still using a core 2 duo. Unless you plan on buying more stuff like a case x-motherboard x-processor x-case in the future you probably would have the best of luck with. I have the same computer with a gtx 550ti in scrap stuff/ stuff I have laying around. They gtx 550ti psu reqiurement is 380w I think if you looked at something like a gtx 650 you would also need a different power supply either 430+ watts 80+ bronze certified or any corsair power supply really. The only thing to note with a lot of dell cases mounting is unique. For example, when I swapped the power supply for my co worker on the same computer there are little fin looking things that slide into the power supply to mount + the normal 4 screws in the back. so I would almost say for 2d even a gtx 550 550ti will be substantial and even overkill. Like this one is used but the description looks good for the condition.
http://www.biturls.com/HsuT1 on ebay atm
thanks a lot for these details!
In fact, i decided to change my graphic card because my PSU is down and old GC is not windows 8 compatible.
So I hope that my new PSU will not be too difficult to adapt to my old dell!
Unfortunately, all PSU corsair I've found have fan on top (so horitontal), instead of vertical. not sure that airflow would be adapted...
Have a nice day!