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.

  • 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.

  • 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.

  • You use USB-C to connect the MacBooks to the Dock, right?
    – nohillside
    Jul 26, 2020 at 18:34

2 Answers 2


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.

  • For future people finding this: Even with a MiniDP-to-DisplayPort cable, macOS (tested on a 2018 MBP13 with Catalina and Big Sur) defaults to 1920x1080 and offers 1600x900. With the Option key I can get 1600x1200 to show up. But nothing larger.
    – mbirth
    May 19, 2021 at 8:51

Yeah indeed, I realized the issue with USB-C, so I ordered a caldigit TS3 plus, that should solve my issues.

Thanks for the help!


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