I have an iMac late 2012 model. Mac OS Sierra I jut received my new Dell U2715H monitor last night and have called dell 4 times. No help. I am connecting via the DP (on monitor) and then on the mini DP on the iMac. It is not connecting or recognizing it at all. (i have had previous external monitor and all works fine. Even still have one external connected now and this will be my third - just replacing older 3rd monitor). I am sure it is the connectivity and how I am doing it. Does anyone know if the DP to miniDp should work. The research I am finding seems like it should.