Ubuntu – External HDMI display detected, but not working

I am using Dell XPS 13 9360 with Ubuntu 16.04. It does not have a HDMI slot, so I have a USB-C-to-HDMI adapter, which is then connected to my monitor: DELL S2240L.

In System Settings > Displays, I can see that the monitor is detected properly and is turned on. If I try to move my mouse cursor out of my laptop screen and into the external display area, I can see the cursor leaving my laptop screen. If I keep moving my cursor further away and try to move back, it takes some time to reappear onto my laptop screen, so there is even the display 'space' for the cursor to move to.

However, the monitor keeps saying "no signal" and therefore goes to power-saving mode. I am pretty sure that the adapter doesn't have a problem because the computer is detecting the monitor. The monitor also works fine when connected to a different (Windows) desktop.

Here is the result for running sudo lshw -C video :

*-display               
   description: VGA compatible controller
   product: Intel Corporation
   vendor: Intel Corporation
   physical id: 2
   bus info: pci@0000:00:02.0
   version: 02
   width: 64 bits
   clock: 33MHz
   capabilities: pciexpress msi pm vga_controller bus_master cap_list rom
   configuration: driver=i915 latency=0
   resources: irq:286 memory:db000000-dbffffff memory:90000000-9fffffff ioport:f000(size=64) memory:c0000-dffff

and xrandr :

Screen 0: minimum 320 x 200, current 3840 x 1080, maximum 8192 x 8192
eDP-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 294mm x 165mm
   1920x1080     59.93*+
   1680x1050     59.95    59.88  
   1600x1024     60.17  
   1400x1050     59.98  
   1280x1024     60.02  
   1440x900      59.89  
   1280x960      60.00  
   1360x768      59.80    59.96  
   1152x864      60.00  
   1024x768      60.04    60.00  
   960x720       60.00  
   928x696       60.05  
   896x672       60.01  
   960x600       60.00  
   960x540       59.99  
   800x600       60.00    60.32    56.25  
   840x525       60.01    59.88  
   800x512       60.17  
   700x525       59.98  
   640x512       60.02  
   720x450       59.89  
   640x480       60.00    59.94  
   680x384       59.80    59.96  
   576x432       60.06  
   512x384       60.00  
   400x300       60.32    56.34  
   320x240       60.05  
DP-1 connected 1920x1080+1920+0 (normal left inverted right x axis y axis) 476mm x 267mm
   1920x1080i    60.00*   50.00    59.94  
   1280x1024     75.02    60.02  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  
DP-2 disconnected (normal left inverted right x axis y axis)

Any suggestions/insights?