XPS 15 7590, U2419H, U421HE, differences, DP MST chain

@noliveira  Yes, you can run a dual 1080p daisy chain like you've described.  Just be aware that if you wanted to run dual QHD (2460x1440) as a daisy chain using a USB-C connection to the first display, then you'd need a USB-C display that allowed you to configure the USB link to only run USB 2.0 data so that your system kept enough video bandwidth available.  If the display always set up the link for USB 3.x and couldn't be configured to do otherwise, the XPS 15 7590 wouldn't be able to run dual QHD that way, since the XPS 15 7590 only supports DisplayPort 1.2 over USB-C, not DP 1.4.  Dual QHD plus USB 3.x over USB-C is possible with DP 1.4, but with a DP 1.2 system you'd need to limit USB data to 2.0 speeds.

Also be aware that you should NOT rely on the U2419HE to be a power source for your system if that's what you were planning.  The XPS 15 7590 is designed for a 130W power source, which is more power than the U2419HE supplies.  That means you have two options:

• Keep the system's power adapter directly connected as well so that it has a 130W power source connected.
• Run the system from the undersized power source by having it rely on the U2419HE.  In this case, the system will respond with slower battery charging and reduced performance, especially when under loads that involve the CPU and GPU.  I wouldn't recommend accepting performance throttling as the norm.

If you want a single cable connection, as of this writing you'd need a Dell dock, since they're the only devices that can push 130W over USB-C as of this writing.  Even that is more than the official USB PD spec allows, so Dell is doing something proprietary on some of its docks and systems to stretch that to 130W, but they haven't done that on any displays as of this writing.  If you want to go this route, the WD19 180W when paired with that system would allow you to run your two 1080p displays and provide 130W to the system; the WD19 130W only passes 90W through to the system, so don't get that version.  Or you can get the WD19TB, which would allow you to run dual displays up to 4K 60 Hz each or triple displays up to QHD each, and it comes standard with a 180W power supply.

In terms of your other questions, yes the display cabinets and the stands are otherwise identical.  The I/O panel is the only difference.  That said, in terms of the panel itself, Dell's panels aren't always consistent even among the exact same display model.  I have a pair of U2717D displays, for example.  One of them made a weird noise when I moved it around, so I requested a replacement.  The replacement had a much more yellow tinge to its panel than the one I was trying to replace, which created an obvious mismatch with the other original display I'd bought that was fine.  This persisted even after mucking around with color settings.  So I returned that replacement instead, and the second replacement had the exact same issue.  I ended up keeping the original pair of displays I got because I decided that panel consistency was more important than squeaks when moving the display.  But I just say this to point out that even if you were to get two identical display models, identical panels isn't an absolute guarantee.