Dell WD15 Dock with 2017 MacBook Pro - Displays question I have a Dell WD15 dock connected to a 2017 MacBook Pro. I have one monitor connected to the dock through HDMI at 1920x1080, and a second monitor connected to the VGA port. However, the monitor connected through the VGA port does not display anything unless the HDMI connected monitor is disconnected.

Is it possible to get both displays showing simultaneously through this dock and these connections, preferably with extended display mode? As far as I can tell from the WD15 manual, 2 monitors should be supported at this resolution.
No, that is not possible with that dock.

The WD15 manual does not state that this is a supported configuration. It is only supported for Windows, not macOS.

In order to do what you want, you'll need a Thunderbolt 3 dock instead of a USB-C dock. This is due to the way the signal needs to be demultiplexed in order to drive two separate displays. Essentially this particular dock uses MST (multi-stream transport) in order to drive separate displays - the MacBook Pro does not support that.