HPE RAM Memory 1 x 4GB DDR4 SDRAM 4 DDR3 2400 SDRAM 726717-B21 at Amazon.com
HP 4GB DDR4 SDRAM Memory Module 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
HP 4GB DDR4 SDRAM Memory Module - 4 GB - DDR4 SDRAM - 2666 MHz DDR4-2666/PC4-21333 - 1.20 V - Non-ECC - Unbuffered - 260-pin - SoDIMM at Amazon.com
Amazon.com: OWC 4GB PC19200 DDR4 2400MHz SO-DIMM Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S4GB) : Everything Else
Samsung 8GB KIT(2 x 4GB) DDR4 3200MHz PC4-25600 1.2V 1R x 16 SODIMM Laptop RAM Memory Module M471A5244CB0 at Amazon.com