Probably a silly question but I’m looking to add 16GB RAM to my current 16GB.  

Dell indicates that these two (among others) are compatible. The “H1” version is what I have two of in my system now. The “E1” seems be be more common. Can anyone explain what the possible difference is between them and if there are any potential side effects of mixing them? Thanks

Micron MTA8ATF1G64AZ-2G6E1
Micron MTA8ATF1G64AZ-2G6H1