TLDR;
buy this -> Kingston Server Premier 32GB 2933MHz Memory
Why
As of 2022-04-10, 128GB of ram from dell.com will cost you $2,540.28 USD. This is more than you need to spend for certified ram, but don’t rush to buy what you think might be compatible.
Dell claims the T150 supports 128gb of memory, and 3200mhz memory, just not together.
NOTE 32 GB x 4 supports 2933 MT/s.
I tried 2 different Nemix types, 3200mhz and 2933mhz but they only worked up to 96GB (maybe because of slow CL?), so don’t buy those either.
Learn from my mistakes, buy this -> Kingston Server Premier 32GB 2933MHz Memory
Update 2023-09-18: I whimsically bought a used Dell T150 thinking it’d save me time building my own server. The iDRAC module can be nice for remote management but overall this is one of Dell’s cheapest servers and it shows.