Thanks Kraszmyl. I used my service tag on the dell site originally, but wasn't sure what I was looking for.
I've done some googling on my XPS 8500 and it appears that the GTX 660 Ti is best I can do w/o a PSU upgrade. Does this sound correct? I don't even understand the terminology to be honest.
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Thank you as well for the continued help. I will open it up tomorrow and find the model number on the PSU. (EDIT: Almost 100% sure it's 460w based on my research so far if that helps at all. Thats the stock psu in this model and I didn't change that.)