tbh the speed difference btn 2666 and 2400 is minimal. you would not notice it.  your pc has only 2 DIMM so you can not run a pair of ram in one slot.  if you can not find ram matching the Dell then try to find the two non-Dell ram that were verified by user to run at 2666, if you still want to reach that speed goal.  they were from Crucial or Micron. BL8G26C16U4B.8FD 2x8GB 8ATF1G64AZ-2G6E1 2x8GB
Hi, I have a Vostro 3670. Here is some specs: Cpu: I7-8700, Gpu: Gtx 1050 2gb. I bought the desktop with 8gb 2666mhz ram, I bought a new ram (same capacity and bus), it now runs dual channel but at 2400 mhz. Any way to run at dual channel and 2666mhz? Thanks
How to run ram at 2666mhz