i could not manage to extend my laptop dell xps 15 9550 through TB15 dock to two monitors (U2717D) in 4K. The max resolution that I got is 2K on each monitor.
I tried all the combo with mDP, DP and HDMI, the best I got is 4K for 1 monitor.
The techcenter assured me that using mDP and DP, TB15 can deliver 4K in dual display at 60hz and with HDMI 4K in dual display but at 30hz.
I got nothing on these from intel HD graphics control panel but only 2K at 59/60hz (which is the max available).
However, on the dell website, the TB15 do deliver 4K in dual display at 60hz.
If anyone managed to configure the 4K resolution in multiple displays, extended desktop (as display mode), please let me know
As a workaround... Try disabling Switchable Graphics in BIOS. Part of the problem for me on Dell Precision 7710 (AMD/Intel video) had to do with unable to display 3 external monitors concurrently with Laptop's monitor (for total of 4). I made sure I was running latest firmware of laptop and followed the docking station's driver/firmware updates (found elsewhere here), and I have far fewer issues. I also found that the hub's Realtek GB Ethernet only ran at full 1GB speed when the power plan for Winidows 10 was set to High Performance.
With my XPS 15 9550 and TB15, I can't drive two external displays anymore, period. I was previously able to drive two 4K displays in a very unstable way. Now I am lucky if one of them will work.
I have the exact same problem.
My best guess is that Dell disabled this 'feature' via Drivers in order to create a more stable experience all together. It's quite unfortunate. As this dock has had so many problems, I'm thinking it's due to two major hardware issues:
1. The Dock becomes extremely hot
2. The wire most likely wasn't engineered to correctly supported the spec'ed bandwidth. By disabling dual 4k monitors it greatly reduces the throughput needed.
I've had a SIGNIFICANTLY more stable experience with the TB15 lately. I've had to buy a USB3 to DisplayPort adapter (DisplayLink) in order to drive my other monitor. And I have to plug in the bundled Power Adapter so that it isn't drawing power from the Dock. But it's a small price to pay to get some use out of the Dock.
For anyone looking to purchase this Dock, I recommend getting a StarTech Thunderbolt3-to-DualDisplayPort adapter instead. Use the Laptop Charger, and get a USB3+Ethernet hub and you'll be set. It'll work better than the TB15 and cost half as much.
The benefits of the TB15 don't work as advertised so in the end it's not worth buying. (Cannot use it to charge the laptop and expect stable performance. Cannot drive Dual 4k Monitors. Ethernet and USB3 controller drop if too much bandwidth is pulled over the USB-C cable.)
I thought Dell was releasing a new USB3.1/Thunderbolt3 cable for this dock. Anyone know where I could purchase the cable? As I suspect it's the cable that is the problem, replacing it with the newew model might help.
I watched a video about the Kingston USB-C Dock. The reviewer stated they called Kingston about a problem they noticed with the displays and poor performance. It appears the Kingston dock will purposefully downgrade itself if ANY USB device is plugged in at the time the Dock is powered on. Not the laptop, but the Dock itself.
I thought perhaps the Dell TB15 dock might do the same thing. I unplugged the Ethernet cable, and my USB devices. I plugged in my two DisplayPort 4k 60hz monitors. Unplugged the Dock power cable. Plugged the power back in. Plugged the USB-C connector into my Dell XPS 15 and viola, the TWO 4k Monitors turned on. So it seems the Dell TB dock does the same thing.
Sadly, after a few minutes one of the 4k displays turns off, but I couldn't efven get them to turn on via the two DisplayPort outputs before. I'll have to go back to using the regular DisplayPort out, along with a USB-C to DisplayPort cable (which uses DisplayPort Alt Mode) to get dual 4k monitors again.
I thought this may help anyone experiencing issues whether it be with a single 4k monitor, or perhaps with slow USB devices. The Dock seems to allocate it's bandwidth differently depending on what's plugged in to it upon it being Powered On. (You have to pull the Power cable and plug it back in for it to reset itself).
I was excited for a whole 120 seconds until the Monitor went black. What is amazing is that the XPS 15 stills SEE's the two monitors and reports it as being there. It isn't disconnected from the system, it's just black.
After researching the amount of bandwidth needed by two 4k monitors at 60hz I'm not surprised a single Thunderbolt 3 chip cannot handle everything. Two 4k monitor's is 36 Gigabits/second of data.