Dell specs says memory support max at 2400 MHz with 7th gen CPU and at 2133 MHz with 6th gen CPU. Intel says the same thing, memory max clock is 2400 MHz for 7th gen CPU. You can use higher clock memory but it will downclock to 2400 MHz.  It's just a specs, not limitation. Slower clock memory 2133 MHz will work with 7th gen CPU in the 3620.  If that was your concern.
This might be an easy one, but I couldn't find an answer. Dell says 7th Gen CPU only supports 2400Mhz RAM. Intel says their i5-7500 supports both 2133Mhz and 2400Mhz. I have both on the way, a Precision 3620 and an i5-7500. Is what Dell says a Dell limitation, or does the the i5-7500 support both speeds in a 3620? From the 3620 Tech Guide: [IMAGE] From Intel for the i5-7500: [IMAGE] I'm also looking to add RAM, but don't want to screw it up, even though I can return it.
Precision 3620 RAM speed vs. CPU