I am the owner of a DELL WD15 Dock and a Dell U3818DW monitor.
I bought the dock to quickly switch between both of my macbooks…. But seems happen to not work as I'd like to.
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On my Macbook Pro 2017 13", on Mojave 10.14.6, on the display options, if I press "option + scaled" to get the full list of available resolutions, I can get 3840 x 1600. On that one, the dock works like a charm.
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On my Macbook Pro 2018 15", on Catalina 10.15.5, the maximum resolution I can get is : 1920 x 1080. But it works if I use the HDMI apple adapter (but it is not handy to unplug the monitor from the dock every time).
Has anyone ever faced that situation? Please tell me you found a solution! ?
Thank you anyway, and have a great day,
PS : the monitor is connected with HDMI.
Best Answer
The limitation is the Dell WD15 Dock only supports HDMI 1.4a (see specifications), which only supports 3840 x 1600 at 24p, and the dock does not support HDCP (content protection). Your Mac wants to run at 60p unless it is playing a movie, in which case Netflix wants HDCP. Count yourself lucky that your 2017 Mojave Mac will let you use 3840 x 1600 at all.
The fix is to use DisplayPort. Get yourself a mini-DisplayPort to DisplayPort cable (around $10) and use that to connect your dock to your display and you should be able to get the full 3840 x 1600 at 60 Hz support.