Timetec DDR4-2666 8GB Replacement for Synology D4ES01-8 DDR4 ECC Unbuffered SODIMM 2666MHz PC4-21300 260 Pin 1.2V CL19 Memory RAM (Compatible for RS1221RP+, RS1221+, DS1821+, DS1621xs+, DS1621+) at Amazon.com
Kimtigo DDR4 2666 8G Laptop Dram 2666MHz (PC4-21300) CL19 (Compatible with 2400MHz or 2133MHz) 1.2V Notebook 1Rx8 Single Rank 260 Pin SODIMM Laptop PC Computer Memory RAM(8GB) at Amazon.com
Patriot Viper 3 Series, Black Mamba, DDR3 8GB (2 x 4GB) 1600MHz Dual Channel Kit (PV38G160C9K) at Amazon.com