XPS 8910, confused about expanding memory, #2

I have the same model, XPS 8910, bought in May 2017.  Sys config on Dell.com showed "370-ACTN : 16GB (1x16GB) DDR4 2133MHz SDR AM Memory" so I bought another for the upgrade and it didn't boot at all. So I pulled the original and saw that it was a 16GB (2rx8GB) so I bought one of those and it still didn't boot. So I put the new one where the old one was (DIMM 1 with white clip) and everything worked with just the new module in the system. So then I put new module in DIMM 3 (black clip) and the original in DIMM 4 and the system booted. Bios recognized the new memory and then I booted into windows with no problem. And per 9Legend's question about why someone would need this much....I am not sure I do but, I have 4 people that have profiles on my desktop and they are always leaving stuff open and they never sign out. And it always seems like Windows was reluctant to use the last 4GB of memory and the Pagefile was constantly being hit and PC was getting really sluggish. So, I thought I would throw memory at it and see what happens. I  should have waited to write this to see if it indeed helped my situation but if I waited I probably would have forgot. No matter where you go, there you are.