I just installed Ubuntu 18.04 (was using Elementary OS before) on my Dell Latitude, which has two monitors connected via a DisplayLink dock. I managed to get three screen (laptop screen + two external) working on Elemantary OS after installing the DisplayLink drivers from the Dell website. On Ubuntu 18.04 I am not seeing the external monitors, even though I managed to install DispplayLink drivers.
I have tried with NVIDIA proprietary drivers (nvidia-driver-390) and with X.Org nouveau (xserver-xorg-video-nouveau).
EDIT (Oct 2018): Installed the latest Dell DisplayLink driver which says it is working with Ubuntu 18.04 from http://www.displaylink.com/downloads/ubuntu Issue remains.
Another issue, possibly related: I can only boot into Ubuntu using "Ubuntu on Wayland", the default Ubuntu just goes right back to the login screen after I type in my password.
$ lspci -k
00:00.0 Host bridge: Intel Corporation Xeon E3-1200 v6/7th Gen Core Processor Host Bridge/DRAM Registers (rev 05)
Subsystem: Dell Xeon E3-1200 v6/7th Gen Core Processor Host Bridge/DRAM Registers
00:01.0 PCI bridge: Intel Corporation Skylake PCIe Controller (x16) (rev 05)
Kernel driver in use: pcieport
Kernel modules: shpchp
00:01.1 PCI bridge: Intel Corporation Skylake PCIe Controller (x8) (rev 05)
Kernel driver in use: pcieport
Kernel modules: shpchp
00:02.0 VGA compatible controller: Intel Corporation Device 591b (rev 04)
Subsystem: Dell Device 07d0
Kernel driver in use: i915
Kernel modules: i915
00:04.0 Signal processing controller: Intel Corporation Skylake Processor Thermal Subsystem (rev 05)
Subsystem: Dell Xeon E3-1200 v5/E3-1500 v5/6th Gen Core Processor Thermal Subsystem
Kernel driver in use: proc_thermal
Kernel modules: processor_thermal_device
00:14.0 USB controller: Intel Corporation Sunrise Point-H USB 3.0 xHCI Controller (rev 31)
Subsystem: Dell Sunrise Point-H USB 3.0 xHCI Controller
Kernel driver in use: xhci_hcd
00:14.2 Signal processing controller: Intel Corporation Sunrise Point-H Thermal subsystem (rev 31)
Subsystem: Dell Sunrise Point-H Thermal subsystem
Kernel driver in use: intel_pch_thermal
Kernel modules: intel_pch_thermal
00:15.0 Signal processing controller: Intel Corporation Sunrise Point-H Serial IO I2C Controller #0 (rev 31)
Subsystem: Dell Sunrise Point-H Serial IO I2C Controller
Kernel driver in use: intel-lpss
Kernel modules: intel_lpss_pci
00:15.1 Signal processing controller: Intel Corporation Sunrise Point-H Serial IO I2C Controller #1 (rev 31)
Subsystem: Dell Sunrise Point-H Serial IO I2C Controller
Kernel driver in use: intel-lpss
Kernel modules: intel_lpss_pci
00:16.0 Communication controller: Intel Corporation Sunrise Point-H CSME HECI #1 (rev 31)
Subsystem: Dell Sunrise Point-H CSME HECI
Kernel driver in use: mei_me
Kernel modules: mei_me
00:17.0 RAID bus controller: Intel Corporation SATA Controller [RAID mode] (rev 31)
Subsystem: Dell SATA Controller [RAID mode]
Kernel driver in use: ahci
Kernel modules: ahci
00:1c.0 PCI bridge: Intel Corporation Sunrise Point-H PCI Express Root Port #2 (rev f1)
Kernel driver in use: pcieport
Kernel modules: shpchp
00:1c.2 PCI bridge: Intel Corporation Sunrise Point-H PCI Express Root Port #3 (rev f1)
Kernel driver in use: pcieport
Kernel modules: shpchp
00:1c.4 PCI bridge: Intel Corporation Sunrise Point-H PCI Express Root Port #5 (rev f1)
Kernel driver in use: pcieport
Kernel modules: shpchp
00:1f.0 ISA bridge: Intel Corporation Sunrise Point-H LPC Controller (rev 31)
Subsystem: Dell Sunrise Point-H LPC Controller
00:1f.2 Memory controller: Intel Corporation Sunrise Point-H PMC (rev 31)
Subsystem: Dell Sunrise Point-H PMC
00:1f.3 Audio device: Intel Corporation CM238 HD Audio Controller (rev 31)
Subsystem: Dell CM238 HD Audio Controller
Kernel driver in use: snd_hda_intel
Kernel modules: snd_hda_intel
00:1f.4 SMBus: Intel Corporation Sunrise Point-H SMBus (rev 31)
Subsystem: Dell Sunrise Point-H SMBus
Kernel modules: i2c_i801
00:1f.6 Ethernet controller: Intel Corporation Ethernet Connection (5) I219-LM (rev 31)
Subsystem: Dell Ethernet Connection (5) I219-LM
Kernel driver in use: e1000e
Kernel modules: e1000e
02:00.0 3D controller: NVIDIA Corporation GM108M [GeForce 930MX] (rev a2)
Subsystem: Dell GM108M [GeForce 930MX]
Kernel driver in use: nouveau
Kernel modules: nvidiafb, nouveau, nvidia_drm, nvidia
03:00.0 Network controller: Intel Corporation Wireless 8265 / 8275 (rev 78)
Subsystem: Intel Corporation Wireless 8265 / 8275
Kernel driver in use: iwlwifi
Kernel modules: iwlwifi
04:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. RTS525A PCI Express Card Reader (rev 01)
Subsystem: Dell RTS525A PCI Express Card Reader
Kernel driver in use: rtsx_pci
Kernel modules: rtsx_pci