XPS 15 9500, WD19TB, dual 4K monitor 60Hz issue

@timfur  Not sure it's a known issue, but the XPS 13 9300 is having dual 4K 60 Hz issues with the WD19TB dock.  Unclear as yet whether it's general issues with dual 4K displays or something specific to the combination of that system and the WD19TB.  But the XPS 15 9500 may have some parts/firmware in common with that system.  Just as one thing that may have been overlooked, have you updated the firmware on the WD19TB itself?  You can get that from its downloads page here.  Apart from that, you may just need to keep an eye out for drivers or (more likely) firmware updates.  Since this is a recently introduced system, chances are there will be a few coming out in somewhat quick succession.  Seems to be the norm these days now that practically everything can be patched later on.

Yeah, I've got the latest firmware on the dock. Checked this a few times as I was experimenting.  You're saying it's new hardware, not that new though for such an annoying issue to persist. I won't hold my breath waiting for the new drivers. Possibly the dock is glitchy? It's the Intel's UHD driver that reads out the supported modes, how does it get them  from the mons plugged into the dock? Maybe just exchange the dock.

Btw, if I plug in the 2nd mon directly into the laptop instead of downstream tb, it works just fine, as expected. Swapping the monitors or cables doesn't do any good either. It's the behavior of this downstream tb port on the dock.

I have similar issue on same configuration. I have a Dell XPS 9500 (15-inch, 2020) connected to the Dell WD19TB via one of the TB3 Ports on the left side and two LG 27UK650-W displays connected to the dock. One display is connected to the Fullsize DisplayPort and second display is connected to the expansion/downstream TB3 Port via an TB3-DisplayPort adapter.

I get both screens working in 4K@60Hz only if I hot-plug (power-cycle) the second display. The second display reverts to 30Hz if it is connected while the XPS 9500 is restarted or removed from the dock. Quite annoying.

This should work out of the box because the WD19TB manual states that dual 4K@60Hz should work when the second display is daisy chained to the downstream TB3 on the dock.

Meaning you can plug in a 4K display to any of the 4 available ports on the dock (two fullsize DP, USB-C/miniDP or HDMI - although HDMI 4K@60Hz is rare on a display) and you can plug in the other display to the downstream TB3 on the WD19TB.

Totally a bug. I have updated all the drivers and firmware for the dock as of the comment. Doesn't work.

P.S: I am on Windows 10 Pro, but I tested that the workaround of hot-plugging the second display in Ubuntu does not work, so its downhill from Windows 10, but they don't support Ubuntu officially.

I am the same person as @raisedadead , I for whatever reasons could not merge my duplicate accounts.   I will be using this one henceforth.

Anyways, just an update that I have now gotten into even weird behavior since a few days. Here is the config and the behavior for me with the Dell Thunderbolt Dock – WD19TB and the Dell XPS 9500 (15-inch, 2020):

As a reminder, I have two LG 27" 4K HDR Displays (27UK650) with DisplayPort 1.2, where Monitor one is connected via a full-size DisplayPort on the dock and the Monitor two is connected via a Thunderbolt 3 to DisplayPort adapter.

1. Laptop on + Dock hot-plugged in - Monitor 1 runs 4K at 60Hz. Monitor 2 runs 4K at 30Hz

2. Laptop to sleep and the wake up + dock already connected (connected before laptop went to sleep) - Monitor 1 runs 4K at 60Hz. Monitor 2 runs 4K at 30Hz

3. Laptop restarted/booted from cold + dock already connected - Monitor 1 runs 4k at 60Hz, Monitor 2 runs at 60Hz

This is getting crazier and annoying by the day.

XPS 9500 10th Gen i7 8 cores, Nvidia GTX 1650 4G GDDR6, 1 TB SS drive, infinity edge touch screen UDH (4K), 32 Gigs RAM, did not get the i9 as it has heat issues which means the fan runs all the time under load.

Had my new XPS 9500 for 3 long weeks and glad I have Pro support! Same issues with the clack y track pad, little bleed of light to the left bottom, screen black outs which I resolved by uninstalling Dell monitor control panel but I am still getting sudden black out screens that I have to fix by right clicking on the screen and resetting my screen preferences. Done that a dozen times. Since I do photography I have a 32 inch 4K external monitor and a HD monitor used to extend the laptop monitor. This works great in Lightroom except I cannot get my 4K monitor to run at 60Hz. Might as well use the HD that runs at the full 60 Hz refresh rate. Many hours later Dell got this fixed once and then it got unfixed again. At 30Hz doing photos is really slow refresh rate. When I do plod my way through photos I notice that my power went form 100% to 90% in an hour. I have an Dell WD19TB which supplies the power to the laptop. Many discussions about replacing this for the 3rd time.

Dell support really hung in there with me through the last 3 weeks. Since my photo external backups drives are 3-4 years old I decided to update to a WD Ultra USB-C. That is when I found out the USB-C port on the right side did not work. It also does not see external SS drives.

Fan noise not too bad especially when I am deep in the woods doing photo development. It runs a lot but not too loud or hot. (recommend the i7 over the i9 with know issues for getting really hot)

Having used every combination of power settings the laptop just will not shut down. If I leave the lid slightly open sometimes I get to use the power on button but not so much.

Some of the issues may be driven by the incredible worst upgrade that Windows 10 has forces on users...build 2004. I know the hardware manufactures like Intel, NVIDIA, etc. are going nuts trying to troubleshoot all the new windows useless features and endless updates. I know this because in two weeks I have done these update 2 times: flashed the BIOS, updated all the chipsets, audio/video drivers, network, serial ATA, apps...etc. Really update the entire system every 2 weeks. However, it must be done.
Sigh...Dell told me that they are going to replace my motherboard this week but hopefully the tech that comes out knows DO NOT TOUCH THE HARD DRIVE! This is kind of like getting a new computer isn't it?

Again Dell Pro support has been fantastic at trying to run this to ground. Maybe Dell needs to slow down their production of this top of the line XPS to solve some of these issues before they send out the laptop. Why am I keeping it? This laptop is state of the art and somewhat the future with TB3 all around. I also have used Dell laptops for many years and this is the first time I have had so much trouble. Hope replacing the motherboard fixes the problem as there is no guarantee a new one will be any better.

@mrugesh.m , @timfur 

Can you try your dual 4K setup connected to both the DP ports on the dock?  Or some combination of DP + HDMI or  HDMI + TB? wonder if this would be a work around...I'm in the middle of purchasing the same setup ( XPS15 9500/disc graphics + WD19TB + Dual 4k)...

Like others mentioned the setup technically works with its own annoyances. The DP ports will run 4K but to get 60Hz you are limited by the bandwidth and hence need to use the Upstream TB3 - this is mentioned in their user manual with an asterisk (Dell chose to make it very convenient for them and mislead people who do not understand tech jargon). Their support reached out on a private DM, and so far it doesn't even look like they know their own product. I had point them to the bandwidth limitation on the dock. Anyways, I have listed all the scenarios that I came up with and their results in a previous comment. Please free to check them before purchasing and making a decision.

I gave up on this Dell dock with XPS9500. 2x 4K60Hz setup is not reliable. It works with the downstream TB3 setup after a full reboot. But once laptop is undocked it never comes back at 60Hz when docked back in. I returned this Dell dock and got another one from a different brand and it works fine 2x4K60Hz via DP. There's a tradeoff on power though as XPS9500 needs 130W. So I had to accept a slow-charge mode (or plugging in a power cable) in exchange for sane behavior. Fine by me. Also WD19TB is noisy with the built-in fan revving up and down all the time. Looks like they took some shortcuts in designing and developing this product.

@timfur  Issues I'd seen reported with the XPS 13 9300 and XPS 15 9500, particularly around the USB-C/TB3 ports, are partly why I ended up getting a ThinkPad X1 Extreme Gen 2.  (Other reasons include that I didn't want a system with just USB-C/TB3 ports and wouldn't have been able to put up with the way Dell relocated the Home/End keys to the top row rather than the arrow keys.)  The X1E is similarly power-hungry (it's designed for 135W), but Lenovo address that on their Thunderbolt 3 Workstation Dock Gen 2 by having a system-side connector that includes a USB-C/TB3 connector and Lenovo's slim tip power connector, the latter of which can supply up to 170W.  The two connectors on that "combo connector" are also only attached magnetically, which means you can still use the dock with other systems by connecting only the USB-C/TB3 connector, in which case the dock can provide up to 65W over that connector.

@timfur if you do not mind could you share the details for the Dock that you ended up going with. I am intending to return the WD19TB as well.

Dell's support doesn't have a clue about their own product and do not read their own literature. They have been DM-ing me back and forth and all they keep circling back to is use the "correct" cables and ports.

On one occasion, I had to point them to their manual saying - "hey your documentation says: Dual 4k@60Hz will only work when you have the second monitor connected to downstream port". What hilarious is they asked me to troubleshoot by replying this: "Do we have another dock of similar model? Or laptop that can be swapped and tried and check if the same things happens on the other set up as well" - It's just sad and funny that support team expects an end user to do this.

I have the exact same issue as the OP.

The dock is plugged into the XPS9500. Once I unplug the dock from the laptop and plug the dock back into the laptop, the monitor on the upstream TB/USB-C comes back at 30Hz with no 60Hz mode available. 

If however, I unplug both display from the WD19TB, plug the laptop into the dock, plug the first monitor via the thunderbolt upstream port first, then after that I plug the second monitor via display port cable, I get  60HZ on both monitors.

As soon as I unplug and re-plug the laptop, only one monitor will have 60hz. The other is stuck in 30hz mode without any chance of 60hz.

Of course I updated all BIOS drivers + the DOCK hast the latest FW.
Setup:

2 Eizo EIZO EV2785 ( 3840x2160 4K)
Dell XPS 15 9500
WD19TB

I tried every possible solution regarding cables:

Connected the displays with two USB-C to DisplayPort cables 
Connected one display with USB-C to USB-C, the other with USB-C to DisplayPort
Connected one display with USB-C to USB-C, the other with USB-C to HDMI
etc etc.

Always the same outcome.

The issue is related to the WD19TB only.
I bought a "HP Thunderbolt Dock 120W G2"  to test and with the HP dock its working reliable (I always get 2X 60HZ @4K). Unfortunately, the HP only charges my laptop at 90W, so its not perfect. At least the display works reliable.

I have exactly same issue. But when I hot plug my older XPS 15 9570 to dock I have no issues whatsoever, both 4k monitors working @ 60hz.

Is there a reason so many ppl have issues with the docking stations for connecting monitors?  Makes it tough when i want to connect three of them with so many ppl having these issues.

Exact same issue here, still no fix from Dell??
Have updated all drivers etc.

My XPS 15 9570 doesn't have this issue at all using the WD19TB and I can replug and get 2x 4K 60Hz immediately.