This worked with much fiddling on 15.10, but since upgrading to 16.04, I can't get the 2nd monitor working at all.
xrandr -q
Reports "HDMI1 disconnected" though it isn't.
With open source drivers, only the primary notebook monitor works, and with nVidia proprietary drivers, X can't boot at all.
Maybe a good config of xorg.conf could fix it, but I'm no expert at that. Anyway, has anybody found a fix for Dell 3543, or does anyone at least have some clue where to begin fixing it?