[NAME]  "A 6 pin PCIe power connector can in theory be plugged in 8940 6 pin ATX socket " In my opinion, this is not good advice. [NAME]-Chris M   [NAME]-BradL  CPU connectors are not GPU connectors. EPS12v and ATX12v are in no way related to 6 pin and 8 pin AUX PCI-E connectors.  The number of pins and what is on them are completely different things. There is no such thing as the number of pins defining what the connector is for.  PCI-E 8 pin plugged into EPS12v 8 pin or vice versa will DESTROY the board and the power supply. The six pin connector for the motherboard on the 8940 is completely Dell proprietary and has nothing whatsoever to do with ATX or EPS12v or TFX etc. [IMAGE]      
8940 stock psu is a modified TFX with dimensions 85x65x225 mm.  (standard TFX is  D500E005P H500EPM-00 0Y7R0X 8.5*6.5*22.5cm [URL] looking at 8940 case, it is not mandatory that psu upgrade has to be TFX in order to fit inside the case. when looking at stock psu, the narrowest dimension of 65 mm wide is the actual physical restriction due to motherboard in proximity, but there is no restriction of a psu to be 85 mm high. In fact it can be quite a bit taller than 85 mm (up to the width of case,169 mm). There is no other component in the case restricting this dimension.  [IMAGE]8940In comes 850 W SFX psu by cooler master, V850 SFX Gold. DIMENSIONS (L X W X H)100 x 125 x 63.5 mmnot only is its width of 63.5 mm comfortably compatible with 8940 case (< 65 mm), its other two dimensions can fit inside the case with ease.[URL] [IMAGE]now user may not be able to screw mount this psu in 8940 case, but looks like it can fit.
XPS 8940, PSU upgrade to 850W that fits inside the case