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jphughan
5 Rhenium

Re: XPS 15 9570 - Use Dual Displays + Laptop Display in Extend Mode

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@Adamman125  ah ok.  In that case, yes you can use a daisy chain setup.  However, note that the video bandwidth available in a daisy chain setup depends on a few factors.

- If you set up a daisy chain using a USB-C to DisplayPort cable to connect to Display #1, then you can run dual displays up to 2560x1600 each.

- If you set up a daisy chain using a USB-C to USB-C cable to connect to Display #1, then the bandwidth available depends on how that display uses its USB-C input.  If it uses it to support video and only USB 2.0, then you can use dual displays up to 2560x1600 each from that connection, just like a USB-C to DisplayPort cable setup.  If on the other hand it configures the USB-C interface to support video and USB 3.x, then you'll only be able to run dual displays up to 1920x1200 each, because carrying USB 3.x over the USB-C interface cuts your available video bandwidth in half.

- Technically a Thunderbolt 3 daisy chain also exists, but you can only create that if you have a display that actually has a Thunderbolt 3 input (rather than regular USB-C) and also has a Thunderbolt 3 "upstream" port that you're connecting to a second Thunderbolt 3 display.  That would be a rare setup, but if you had this, you could run dual 4K 60 Hz displays.

- If you want to run a dual display setup that requires Thunderbolt 3 bandwidth levels but you don't have Thunderbolt 3 displays, then you'd need a Thunderbolt 3 to Dual DisplayPort adapter.  Note that there is a separate device called a USB-C DisplayPort MST hub.  It looks similar, even serves a very similar purpose, and costs less -- but it is NOT the same thing.  An MST hub only taps into a single DisplayPort interface available on regular USB-C.  A Thunderbolt 3 to Dual DisplayPort adapter taps into Thunderbolt 3, which gives it access to two DisplayPort interfaces from the system and therefore twice as much bandwidth.

If all of that was a bit overwhelming, perhaps it would be easier for you to just specify what resolution(s) you want to run in your dual display setup?

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jphughan
5 Rhenium

Re: XPS 15 9570 - Use Dual Displays + Laptop Display in Extend Mode

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@Adamman125  in addition to my answer above about display setups without a dock, I also just noticed that you said you want to charge your XPS 15 9570 over USB-C and run a daisy chain setup at the same time.  Since the 9570 only has a single USB-C/TB3 port, I'm assuming you plan to use a display that has a USB-C input and supports providing power?  If so, I wouldn't go that route.  The XPS 15 models are designed for a 130W power source, which is actually more than the 100W official max of the USB Power Delivery spec.  Dell did something proprietary to stretch that to 130W on some of their docks, but I haven't seen any of their displays support providing that kind of power.  Usually displays only provide about 45-60W.  If you try to run your XPS 15 from an undersized power source, you can end up with behavior like slower battery charging and even CPU and GPU performance throttling, especially when both the CPU and GPU are being used.  In extreme cases the system might even continue pulling from its battery to make up the power deficit, but it will throttle performance significantly first in order to try to run "sustainably" from that undersized power source rather than running in a way that could cause the laptop to die even while plugged into power.

So if you want your XPS 15 to perform properly, you'll need to keep its AC adapter plugged into the system's barrel connector -- but of course that means an extra cable.  If you want a single-cable connection that provides adequate power and allows you to run your displays, you'll need a dock.  For an XPS 15 9570, the docks to choose from would be the WD19 with a 180W adapter (not the 130W adapter it can also be ordered which, since that version can only pass 90W through to the attached system) or else the WD19TB, which comes standard with a 180W adapter.  The right dock would depend on the display setup you wanted.  The WD19 with that system can handle dual displays up to 1920x1200 each.  The WD19TB can handle dual displays up to 4K 60 Hz.

Adamman125
1 Copper

Re: XPS 15 9570 - Use Dual Displays + Laptop Display in Extend Mode

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First off, thanks so much for the amazingly detailed response!

I definitely understand much of what you said, although that means we may have exposed some less-than-stellar advertising on Dell's part...

My plan was to daisy chain two Dell UltraSharp 24 USB-C Monitor: U2419HC (so, 1920x1080) together with usb c cables so it would be:

Dell 9570 --USBc--Monitor 1--USBc--Monitor 2

I actually got this idea from Dell's site (https://www.dell.com/en-us/shop/dell-laptops/xps-15-laptop/spd/xps-15-9570-laptop), which states I would be able to charge the laptop and support 2 monitors. If their own monitors can't charge the laptop, do you have any ideas about which can? I'm really trying to avoid a dock and thus another piece of clutter on my already far over-cluttered desk, not to mention those things are really expensive, basically the same price as the monitors themselves!

 

 

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jphughan
5 Rhenium

Re: XPS 15 9570 - Use Dual Displays + Laptop Display in Extend Mode

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@Adamman125  ok, if you're running dual 1920x1080, then a non-Thunderbolt daisy chain setup would definitely work even if you had a USB-C connection to Display #1 and it was trying to run USB 3.x data on that connection.  Your system would still be able to send enough video bandwidth to run both displays.  However, note that to set up a daisy chain, you'd need to use a regular DisplayPort cable to connect Display #1 to Display #2; I believe those displays come with such a cable.  The reason is that the only display output port on those displays is DisplayPort, and although USB-C to DisplayPort cables exist, I believe they only work when connecting a USB-C source to a DisplayPort input.  I don't think you could use them to connect a DisplayPort output to a USB-C input.  But those displays also have a DisplayPort input, so a regular DP cable is fine, and the end result would still be the same.

Charging is going to be a problem, though.  The U2419HC displays can supply up to 65W, which covers the majority of laptops on the market, but not the XPS 15.  And the XPS 15 can run multiple displays and charge itself from the same cable....but only if it's connected to a device that can actually provide enough power and run multiple displays, like a docking station.

You won't find non-Dell displays that can charge that system.  The reason is that the XPS 15 requires 130W, which is above the 100W official max of the USB Power Delivery spec.  Dell has a few docks that can provide that much power because they've done something proprietary to stretch the spec, but that won't be implemented on non-Dell stuff.  I haven't seen any Dell displays that can provide that much power.  So your options would be as follows:

#1 -- Buy a dock.  If you only need dual 1080p displays, you could use a WD19 with a 180W power supply.  But you might want to consider getting a WD19TB just for futureproofing in case you decide to get higher resolution displays later, since the WD19 tops out at dual 1920x1200 with that system, whereas the WD19TB can do dual 4K displays.

#2 -- Use Display #1 as a power source and put up with reduced performance and battery charging speeds.  I don't recommend this.

#3 -- Keep your XPS 15's AC adapter connected to its barrel-style connector in addition to the displays.  Even if you have to buy another AC adapter to dedicate to this purpose, that would be less than a dock.  But it's slightly less convenient, of course.