I can confirm that both Corsair H60 (single fan) or Corsair H80 (dual fan) work quite well with XPS 8950. Temp are approx 5-10 *C less as compared to Dell AIO cooler. The big factor for me is how quiet Corsair units are. If you'll be going Corsair route, be sure to order Corsair LGA1700 kit and reuse your existing AIO mounting bracket. No need to remove motherboard, installation is super simple and straight forward.  
Hello, I have the 8950 with the liquid cooling option and it cools very well but it is more audible than it should be in my humble opinion. It does not bother me too much now but I would like a quieter option in the future when I decide to enroll into an academic program. I searched through XPS and Alienware forums and read that the audible noise is normal so there is no need for a parts replacement.  I decided that I can replace it in the future with a Noctua air cooler (most probably the NH-U12S) but when I watched an installation video, I realized that the technician had to mount a bracket behind the motherboard. I know the 8950 comes with a Z690 chipset and Noctua provides a LGA 1700 tool kit so will it be necessary for me to remove the motherboard or can I use the pre-existing bracket that was already placed with the Dell liquid cooling system? Also, I might need to ziptie the rear Dell fan to the back of the PC since I don't have a 120mm fan bracket. If the fan cable does not reach the motherboard slot then I can buy a rear fan that does not cause a BIOS error. 
XPS 8950, Liquid cooling replacement