Patriot Signature Line DDR4 16GB (2 x 8GB) 2666MHz (PC4-21300) UDIMM Dual Kit Memory Kit PSD416G2666K at Amazon.com
G.Skill Trident Z Royal Series [Silver] 16GB (2 x 8GB) 288-Pin SDRAM (PC4-25600) DDR4 3200 CL16-18-18-38 1.35V Dual Channel Desktop Memory Model F4-3200C16D-16GTRS at Amazon.com
Amazon.com: OWC 8GB (2 x 4GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S08P) : Everything Else