Saying that it comes from Dell changes a lot. Dell are notorious for cutting any corner they can, which means they'll use a cheap case, stock cooling, cheap motherboard and the lowest power rating on the PSU they can get away with. Then again, Dell do cheap computers. To make them cheap, you have to compromise somewhere.
Regarding the PSU: there are two rules for system designers. Always aim for 100-200W above what your system will actually use (according to a wattage calculator at least), and always make sure the PSU comes from a named (and famous) brand. A PSU with no brand is likely to blow up at 70% load or higher (and I've heard of some blowing up at 55% load). Remember that CrossFire/SLI will use a lil more than double the normal amount of power for each graphics card, and produce up to three times as much heat.
I could explain why you never want to put your PSU at 90% load or higher... but I don't think people will listen.
Regarding the graphics: if you're gaming, the graphics is the most important part of the computer (followed by the CPU, the PSU, and the case - in that order). You generally want to push as much money as you can into the graphics card. If you don't have the budget for the card you want, you can opt for using the built in graphics (Intel HD 2000 for the Core i7-2600, HD 3000 for the i7-2600K) and save up for a little while longer, or you can just get a cheaper graphics card. The only reason to use two graphics cards in CrossFire/SLI is to get better scores in Folding@home applications or video rendering, and for both nVidia cards outclass AMD cards (AMD is only good at gaming, so long as the drivers don't get in the way). Not only will using multiple graphics cards increase the power usage/heat generated, but it will also create a graphics stuttering problem that is common in all CrossFire/SLI setups. Put simply, getting one powerful card is better in every respect... that and, in a Dell case, you won't have adequate cooling for two graphics cards AND a Core i7 CPU.
...I think that's all I need to say. The rest is down to how customisable Dell make their computers.