SK Hynix 4GB 1Rx8 PC4-17000 DDR4-2133 1.2volt CL15 260 Pin Sodimm Memory p/n HMA451S6AFR8N-TF at Amazon.com
2 x 4GB (8GB Total) Hynix HMT351U6EFR8C-PB 4GB PC3-12800U Desktop Memory 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
SK HYNIX HMA851S6CJR6N 4GB 1RX16 DDR4 SO-DIMM PC4-19200 2400MHZ Laptop Memory at Amazon.com
Hynix 4GB PC3-10600 DDR3 1333MHz HMT351S6CFR8C-H9 at Amazon.com
SK Hynix 4GB DDR4 2666MHz SODIMM Memory Module at Amazon.com
SK Hynix HMT451S6DFR8A 8GB (2x4GB) 1Rx8 DDR3 SO-DIMM PC3L-12800S 1600MHz 204-Pin Non-ECC CL11 1.35V Laptop Memory 2-Piece Kit HMT451S6DFR8A-PB for Other Laptop Systems at Amazon.com