Hello folks,

I just received my new Dell Precision 5550 mobile workstation with WD19TB Dock (180W). So far im overwhelmed by the haptics and power of this wonderful device and overall my software and stuff is working like a charm! Before asking, theseare my specifications:

BIOS: 1.6.1
CPU: Intel Core i7 10850H, 2,7 GHz
RAM: 24GB (16Gb 2933 MHz + 8Gb 2933 MHz)
GPU: Nvidia Quadro T2000 /w Max-Q
Internal: 1920x1200 IGZO+ non-touch, 15,6 inch
NVMe1: WD SN730 512GB
NVMe2: Samsung Pro 960 512GB
Dock: Dell WD19TB, 180W

extd-Display 1: V7 L27has2k-2e
extd-Display 2: V7 L27has2k-2e
extd-Display 3: V7 L27has2k-2e

All of my 3 external displays are working with WQHD / 1440p - 2560 x 1440 on 60 hz. My cables are high quality cables which are possible to be used as 4k-8k resolutions (tested, worked).
My constellation of connection is as followed:

WD19TB to Dell Prec. 5550 with inbuilt TB3-cable (of dock) to TB-port-1. Extd-Display 1 and 2 are connected via DP 1.4 (Dock outport) to monitor. Extd-Display 3 is connected via USB-C-HDMI Adapter on MFDP Port (USB-C /w DP 1.4). The 3 external displays are working on the full performance. BUT! I can't use my internal display too. 

The specifications of the dockingstation should let it work, since the specification says following:

Display Support with
Thunderbolt input
For a HBR2* PC
3 x FHD @ 60Hz
3 x QHD @ 60Hz
2 x 4K @ 30Hz
For a HBR3 PC
4 x FHD @ 60Hz
4 x QHD @ 60Hz
2 x 4K @ 60Hz

Since, how I read this, there should be 3 (HBR2) or 4 (HBR3) external displays possible without loosing the internal display. Or do I understand this in a wrong way and this is ment to say that "OVERALL" there are just these displays possible? 

I understood that the MFDP-Port have had a own bandwidth-lane and the 3 in series connected ports (HDMI, DP1, DP2) are not able to use 3 external displays on this resolution, so I just changed to the MFDP Port (instead of HDMI) for full resolution on the monitors. 

But if I enable the internal display too (how I understand and would like to use it), 2 external displays decrease the resolution. If I set them high again (WQHD), my internal display just shuts off.

SO! 

I would be happy if I could have some help on this, since this was my requirement to order this powerbeast at all. 

Sincerly, one of a new dell's. 

Henrik