You're correct, Dell's specs only list configs they tested. Doesn't mean other configs won't work, but Dell isn't responsible if an unlisted config doesn't work. I'm confused... You said PC has 32 GB of RAM, but then you said "...selling my 2x32gb..." Did you mean selling 2x 16 GB? Dell PCs can be very fussy about RAM so be careful. Many users around here buy RAM from Crucial (a Micron brand) because they guarantee it works in the model selected or they take it back. Crucial is offering 2x 16GB of DDR5-4800 RAM and other options for XPS 8950 here. So you could just add 2x 16 GB modules to the two you already have. NOTE: The OEM 2x 16 are likely installed in 2nd and 4th slots from CPU, with matching color retention clips. If you install the new 2x 16 in 1st and 3rd slots from CPU and have problems or RAM isn't running at the right speed, move the OEM module from 4th slot into 1st slot from CPU, and install new pair in the empty slots, with mismatched retention clips. Not the way RAM is usually installed, but this has come up on both XPS 8940 and XPS 8950. All RAM will run at the speed of the slowest modules installed, 4400 MHz
Purchased 8950 with 32 gb ram as couldn't justify spending addition $400 to get to64gb when you can buy 64gb alone for a little more.  The question is, what's the best way to go about doing this? In the manual, it says you can only achieve 64gb by 2x32gb chips...but I question that as typically with manuals for ram oftentimes they just test certain configs and it doesn't mean others won't work.  The problem is, 2x16gb 4400mhz is hard to find out there so I'm contemplating selling my 2x32gb on eBay to use that money to buy 2x32gb.  Is this the best way to go?  Has someone done this or traversed other methods to achieve 64gb?    
XPS 8950, memory upgrade from 32GB