I updated to Crucial 32GB x 2 later last year.  Also took chance to try the combination with the original SK Hynix 8GB x 2.  No any combination works. 
My XPS 8950 came with 8GB of 4800 DDR5 ram. I ordered.2 x 32gb 4800 DDR5 + 1 x 8gb 4800DDR5 to match (Crucial) However,  I can get the 2 x 32gb recognized at 4400 MHz in the White Dimm slots but when I try to install the two 1 x 8gb chips in the black Dimm slots the computer won't start up with the power button alternating from white to blinking orange. Since the two 8gb chips are different manufactures is this the issue or is it the configuration of 2 x 32 and 2 x 8?
XPS 8950, ram upgrade, 2x8GB and 2x32GB?, #2