Upgrading graphics card, need advice

I didn't know they made a low profile HD3850. You'll have to upgrade your power supply for it. This Seasonic SFX 350w should work, it has the amps for it. Make sure it's the right size to fit in your case before you buy it.

http://www.newegg.com/Product/Prod [...] 6817151063

Does your PSU have a 6pin PCI-Express connector? What resolution is your monitor? What CPU do you have?

How many amps on 12V?

The slim case from Dell uses a TFX form factor power supply. There aren't many you can find, but I'd suggest getting this one http://www.newegg.com/Product/Prod [...] 6817151070 from Seasonic (they make great quality power supplies). It's the highest wattage one Newegg carries, although even then you're only looking at 50 watts more than what you have already......and you'll need to buy a molex to PCIe 6 pin adaptor (such as http://www.newegg.com/Product/Prod [...] 6814999018 or http://www.newegg.com/Product/Prod [...] 6812189120 )

Also, you'll need to to buy a what's known as a "low profile" graphics card. As the name suggests, it's smaller than the normal size cards. As far as I know, there aren't any low profile HD 4850's out there. Do you have a link to the card you want to install?

The top performing low profile card newegg carries would be this 9800GT http://www.newegg.com/Product/Prod [...] 6814187061 It's no 4850, but it isn't too far off. The runner up would be the 9600GT, http://www.newegg.com/Product/Prod [...] 6814162016 or http://www.newegg.com/Product/Prod [...] 6814187060 . The 9600GT's would probably work without having to replace your current power supply, as the 9600GT isn't usually too power hungry.

The 9800GT is a good choice if you choose to go for it. I'd get it over the 9600GT. I've seen the 9800GT work with 250W power supplies ( http://www.pchangout.com/forum/vid [...] e-sff.html ) so I'm pretty confident that it will work with the 300W seasonic I mentioned. It may even work with your 250W, but I wouldn't recommend it. Your mileage may vary though