XPS 15 7590 with WD19TB dock - TB3 drive enclosure won't power up

@ChipFreund  is this the product you're referring to?  If so, I don't think a power output difference would be the underlying issue here because it doesn't look like that product is designed to run from bus power.  First of all, that would be a LOT of hardware to run from bus power.  Second, that product has a connector for an external power supply, so it would have no reason to try to draw bus power.  And third, the specs indicate that it will PROVIDE up to 27W of power to an attached system.  So my guess is that there's some other firmware-level issue that's interfering with a negotiation between that enclosure and the WD19TB, and the enclosure doesn't bother to start until it's negotiated with the device on the other end of the Thunderbolt 3 link.  Just as a sanity check, are you certain you're using the Thunderbolt 3 port near the edge of the dock and not the regular USB-C port near the display outputs?

But if it weren't for those aspects of that product above, a power output difference would be my guess. I don't have an XPS 15 7590, but on my Latitude 7480 I have a BIOS option to determine whether the USB-C port should allow up to 7.5W or up to 15W output.  There's a note that allowing higher output can cause the system to throttle performance sooner.  Annoyingly, the WD19TB User Guide on support.dell.com doesn't mention the power output capabilities of the "upstream" Thunderbolt 3 port, or any of the other USB ports for that matter.  But again, that really doesn't seem like your issue in this case.

@jphughan yes that's the drive unit.  It has an external power supply, but I have read on some reviews on the Akitio site that it draws some power from the TB3 connection as well as the external, which seemed odd to me too, given the claim of 27w power delivery.  Regardless, it works when directly connected to the PC and not when connected to the dock.  I have also started to notice other issues with the dock.  The video drops in and out on the DP on the dock and my mouse and kb (USB) work sometimes and not others.  All in all, I think you may be right about a driver/firmware issues, or perhaps an outright compatibility issue.

@ChipFreund  the USB Power Delivery spec allows power to flow in either direction, but not both -- so it wouldn't be possible for the enclosure to draw power over TB3 while providing it.  Even if it were connected to a system that didn't support being charged over USB-C, I could maybe see it drawing some nominal current over the link, but not enough for the enclosure to rely on for proper operation.  Most systems with USB-C ports only allow output of either 7.5W or 15W max, even if they support significantly higher input to charge themselves.  Given that this product is already using an external power supply, it wouldn't make sense to undersize it by 7.5 or 15W and rely on making up the difference from the attached system.  There are some devices that support wall power if needed but also support running purely from bus power if connected to a system that provides enough, so in theory this enclosure could work that way, but even 15W wouldn't be enough to run that type of enclosure.  According to the Akitio website, the external power supply's output is 12V at 10A, which is 120W.  Even if you subtract the 27W it can provide to an attached system, it's still clearly using a lot more than 7.5-15W.

If you have a USB-C multimeter like this one, you could actually check the wattage running across the link, but I think at most you'd see some nominal amount of power.  I have that device and another similar device for USB-A mostly just for fun because they're not very expensive and it's interesting to see what devices draw or what power sources can provide.

Anyhow, sorry to hear you're having trouble using this through the dock.  Hopefully a fix arrives sooner rather than later!

after you get the replacement unit, is daisy chaining works fine?

i had the exact same problem, and they sent me the new unit.

Dell support sent a replacement dock and it performed the same as the original unit.  The case has been escalated twice and now it is with level 3 team and we are several weeks into the case and still counting...