Any modern PCI-Express card nine inches or shorter in length. With that in mind however, chances are, your power supply is not up to snuff to accept any additional power-loving hardware. Typically OEMs like Dell will only put in as big enough power supply as is needed for the spec they are building. When shopping for a graphics card, I like to take the power requirement for the card, add 20%, and add that number to the power supply already in the OEM box. So for example, You have a 250w in your box, you want a card that asks for 400w, add 20% to get 80 more watts, combine it all together and get 680 watts. It's create a great buffer. Not to mention some power supplies run best in the 25-75% load range and anything above that, it will suck down more power from the wall than it will be putting out and be wasting a lot of energy in heat.