If you have the Dell 500w psu that has two 6 pin GPU connectors it should be able to support up to i7-10700k, 16Gb ddr4, GTX 1080 Ti, Sata ssd (no optical drive) Load Wattage: 442 WRecommended PSU Wattage: 492 W If cpu is i7-10700 non-k, even better Load Wattage: 387 WRecommended PSU Wattage: 437 W calculated using basic on line psu calculator  physically depends on model of 1080ti.  The founder edition is 10.5” long double slot and it should fit 8940 case which is 12.13” in depth. the Dell 500w psu 6 pin GPU connector (black) has all three 12V wires (brown) connected and is effectively 8 pin. You can use a simple 6 to 8 pin adapter to change one 6 pin to 8 pin. [IMAGE]  
It has a 3060 Ti but I will be putting that in another PC.  Does the XPS 8940 psu and case have enough room, power and connections to take a 1080 Ti with a 6+8 pin? 
XPS 8940, 3060 Ti swap to 1080 Ti?