Upgrade your iMac 27'' 2017 RAM with MrMemory review - Wim Arys
Timetec 16GB Compatible for Apple 2017 iMac (27-inch w/Retina 5K, 21.5-inch w/Retina
Amazon.com: OWC 32GB (2 x 16GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S32P) : Everything Else
Apple Memory Module 16GB DDR4 2400MHz SO-DIMM (2x8GB) - Apple