it sounds like a lousy psu. especially cuz dell/alienware, along with all the other oems always use crappy units to keep costs down...
Dell has used a number of psu oem's over the years, quite a few being Newton/Delta's that, while not the highest quality, are pretty decent.
They use a lot of Hipro's now, I have no idea about their quality, but look at the bottom of the post to see the Silver and Bronze 80+ ratings.
Costs are kept down by the fact that they order them by the 1000's.
A typical 5 rail layout dedicates 2 rails to the pcie connectors, don't know if thats the case with the unit in the Aurora.
If the rail ratings are as specified the op would be pushing just beyond the 36 amp limit provided to the pcie connectors since the 5970 can use 25 amps by itself when running Furmark, and the 5850 will add another 12a or so. http://www.80plus.org/manu/psu/psu_reports/SP454_DELL_H875EF-00_CUSTOM_875W_Report%20(80+).pdfhttp://www.80plus.org/manu/psu/psu_reports/SP609_DELL_N875EF00_CUSTOM_875W_Report.pdfhttp://www.80plus.org/manu/psu/psu_reports/DELL_GM869_875W_Report.pdf