I have a new Dell XPS 13 9370, which I have Ubuntu 19.04 running on.
I bought a USB-C to HDMI adapter (an unbranded eBay one), and tried plugging it in but get "no signal" on the display. I have tried all three USB-C ports on the laptop but all give the same result.
I see this show up in
[ 1318.267181] usb 1-1: new full-speed USB device number 8 using xhci_hcd [ 1318.422827] usb 1-1: not running at top speed; connect to a high speed hub [ 1318.431199] usb 1-1: New USB device found, idVendor=0bda, idProduct=2171, bcdDevice= 1.11 [ 1318.431205] usb 1-1: New USB device strings: Mfr=17, Product=18, SerialNumber=19 [ 1318.431210] usb 1-1: Product: BillBoard Device [ 1318.431213] usb 1-1: Manufacturer: Realtek [ 1318.431216] usb 1-1: SerialNumber: 123456789ABCDEFGH
But nothing shows up in the display settings. I tried the same USB-C to HDMI cable on a Dell Inspiron 7380 under Windows 10, and it also showed up the "BillBoard Device" but did manage to output to the display - so it seems like the cable itself isn't broken.
This Phoronix forum discusses changes in 4.19 of the Linux kernel about USB Type-C DisplayPort Alternate Mode driver support, but says that some more work still needed to be done apparently. 19.04 has Kernel 5.0.0, so those changes at least presumably are included. Is the Dell XPS 13 9370 expected to work with HDMI from the USB-C ports under Linux? I haven't yet tried this exact machine with Windows to rule out a hardware issue.