XPS 9570 and WD19TBS

Just to follow up, I connected two external monitors.  Now seeing the AW3821DW at 60Hz refresh rate (3840x1600) and the other monitor (AOC 31.5) at 60Hz (2560x1440).  No idea why I can't get the 60Hz refresh rate when using just a single external monitor.

@Andman99  Not sure what's going on there, but fyi the XPS 15 9570 is a DisplayPort HBR2 system.  The specs you were quoting from the manual apply to an HBR3 system.

@Andman99 

One other thing to consider. The AW3821DW supports G-Sync. That requires a DisplayPort signal. There's a variation of G-Sync meant for LG OLED TVs, which uses HDMI, but that requires a 16 Series or above GPU and also appears to be HDMI VRR. So for best results with your AW3821DW, you might want to use a DisplayPort output on the dock anyway.

In terms of the original issue, make sure you've updated the BIOS, Thunderbolt controller firmware, and dock firmware.  If you have, then this may be an interop issue that still hasn't been fixed. They do occur. Dell's XPS 13 9300 couldn't run dual 4K 60 Hz displays through a WD19TB for a long time even though that should have been possible. But again you might want to consider DisplayPort for that display anyway. I realize that's a workaround and not a fix that identifies the underlying problem, but since I don't have that equipment to test with myself and haven't seen this reported elsewhere, I can't offer a full solution.

@Andman99  Never mind on my last post.  The display does support G-Sync, and G-Sync does require DisplayPort, but G-Sync also requires the NVIDIA GPU to have direct control of the display outputs, and on the XPS 15 9570, the Intel GPU has direct control of all display outputs, with the NVIDIA GPU working indirectly as a render-only device through NVIDIA Optimus.  So you can't run G-Sync from that system at all.  Sorry about that.

@jphughan Many thanks for the reply.  The Dell tech told me it was HBR3, so thanks for clearing that one up. 

I've updated all drivers, BIOS and firmware.  It's a real mystery why the 9570 HDMI port can achieve 85Hz on the AW3821DW, but only 30Hz via USB-C TB WD19TBS.

@Andman99  If I had a dime for every incorrect bit of information I've seen people say they were told by Dell sales/support....  One of the most egregious I remember was a person who was having trouble using a USB-C to HDMI adapter with his XPS 13.  The support person told him that since the XPS 13 was a "high-end system", it could only run external displays through a dock, not a basic dongle.  The true issue turned out to be a firmware problem that was fixed with a BIOS update months later.  I also remember somebody reporting having been told that the XPS 13 can only run 4K external displays if you order the 4K built-in display, which is completely false.

The XPS 15 only gained HBR3 support with the new 9510, because Dell thus far has stuck to giving the Intel GPU direct control of display outputs, and Intel GPUs built into the H Series CPUs used by the XPS 15 didn't gain HBR3 support until Core 11th Gen Tiger Lake.  (Making things even more exciting, for Core 10th Gen, only the "Ice Lake" 10th Gen CPUs had a GPU with HBR3 support.  The Core 10th Gen "Comet Lake" CPUs stuck with HBR2 GPUs.  But both were called 10th Gen.)  On the XPS 17 9700, which uses Core 10th Gen Comet Lake CPUs, if you order the system with an RTX GPU, you get a BIOS option allowing you to choose which GPU controls the outputs, and if you choose the NVIDIA GPU, it becomes an HBR3 system.  But if you order it with a GTX GPU, that option isn't available.  The XPS 17 9710 is always an HBR3 system since it uses Core 11th Gen.

@jphughan Interesting.  Well, I've gone for a DP KVM switch that seems to be working ok.  I now get 85Hz from the WD19TBS.  Annoying, but it works.