So what's the plan here: Remove 1x 8 GB and install 1x 32 GB?  As the XPS 8940 specs indicate, 1x 32 GB will not run in dual-channel mode. So consider 2x 32 GB, as a matched pair, or 2x 16 GB matched pair. And what you're asking is almost impossible to answer because Dell uses various brands of RAM. So if Dell uses brand X and that works in some other motherboard, it doesn't necessarily mean Dell's brand Y will also work. And even if it does work, RAM speed will depend on the CPU, chipset and new motherboard specs too.
I got a coupon from Dell which gives me 10% discount on RAM. So, for one stick of 32 GB UDIMM 3200MHz I would have to pay CAD 215.09 while on Amazon.ca it costs CAD 226.45. Should I buy Dell original? Another concern: if I want to build another PC myself, capable of using 3200 MHz RAM - will original Dell RAM or Crucial RAM be more likely to work without issues? Dell: Dell Memory Upgrade - 32GB - 2RX8 DDR4 UDIMM 3200MHz Amazon.ca: Crucial RAM 32GB DDR4 3200 MHz CL22 Desktop Memory CT32G4DFD832A
I can get original Dell 32 GB cheaper then Crucial - should I buy it?