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

@ksrw395  one more bit of advice in addition to my reply above: I'd really think twice about whether you want QHD resolution on a 24" display.  That creates a very high pixel density that might be tricky to work with without enabling display scaling.  Some Windows applications don't work with display scaling very well at all, but Windows itself can look very bad if you end up using multiple displays with different scale factors simultaneously.  If your built-in display is 1080p, I'm guessing you're not using any display scaling at all (i.e. 100% scaling), so if you plan to run that display and external displays simultaneously, you'll really want to choose external displays that won't require any display scaling either.  I can go into more detail on why trying to use multiple scale factors simultaneously is bad if you'd like, but suffice it to say you really want to avoid that.  QHD resolution is typically found on 27" displays, and in fact even that setup is higher pixel density than the common 24" 1080p setup.  Here are some numbers for context:

- Windows has always been designed to assume a baseline display density of 96 pixels per inch.  With that type of display and a 100% scale factor, something that's supposed to be 1" wide in the real world would appear 1" wide on the display.

 - A 24" 1080p display is 92 ppi, so things are a bit larger and grainier than that baseline.  A 27" 1080p display (rare, but they exist) is even worse at 82 ppi.

- A 24" 1440p display is 122 ppi, which is 33% more dense than "intended", so things at 100% scaling will be quite a bit smaller than normal, which could be uncomfortable to use.  By comparison, a 27" 1440p display is 109 ppi, i.e. 13.5% more dense, so things will still be a bit smaller (and sharper) than "intended", but it won't be nearly as bad.

- Your 15" 1080p display in the XPS 15 is 147 ppi, but that's common on laptops because people's faces tend to be much closer to their laptops than to their external displays, so it's not nearly as much of an issue there.

I personally run an XPS 15 with a 1080p display and dual 27" QHD displays and I think the setup is fantastic.  I can use 100% display scaling across the board, so I don't have any general scaling issues or any of the even worse multiple scale factor issues.  Since you specifically mentioned productivity, I'll give you one perk I discovered about 27" QHD displays:

If you have Windows set to 100% scaling, open Word, and set Word's zoom level to 105%, then your page as viewed in Word matches its real world size, and QHD resolution is enough to view two pages side-by-side in their entirety, including margins, in either portrait or landscape orientation (the pages in the document, not the display itself), and STILL have enough display area for the toolbars above and the status bars and Windows taskbar below.  The same is true in Adobe Acrobat, incidentally, although there I think you can set the pixel density of your display in the settings, so you can use 100% zoom and it corrects that internally.  QHD on a 25" display would still allow you to achieve these views because of its resolution, but because of its smaller size, the pages won't be real world size, so they might be harder to read.

Thank you for your very detailed replies. 

You mentioned:

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I can go into more detail on why trying to use multiple scale factors simultaneously is bad if you'd like

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Can you please elaborate on this? 

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@ksrw395 wrote:

Thank you for your very detailed replies. 

 

You mentioned:

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I can go into more detail on why trying to use multiple scale factors simultaneously is bad if you'd like

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Can you please elaborate on this? 

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@ksrw395  happy to help.  As for the part you quoted, I actually found an earlier post where I wrote about this.  Read the "Bluriness" section of this post for more info.

Many thanks again for the knowledge. 

I've decided to go for two of these 24" 1080p monitors, and daisy chain everything, similar to your setup. 

https://www.dell.com/en-us/shop/dell-24-usb-c-monitor-p2419hc/apd/210-aqco/monitors-monitor-accessories

In the future I may look into the dock method. 

Hi I know this thread is old, but I'm a bit confused about the capabilities of Thunderbolt 3 on the 9570. I read your above answer, which seems to suggest that powering my laptop via one USB C cable and then daisy chaining two Usb c Dell Ultrasharp monitors together wouldn't be possible? The Dell page for the 9570 says

"Thunderbolt™ 3 multi-use port allows you to charge your laptop, connect to multiple devices (including support for up to two 4K displays) and enjoy data transfers up to 40Gbps, which is 8x faster than USB 3.0. Also includes two USB 3.0 ports."

That is exactly the setup I'm proposing. Would it be possible using only usb c assuming both monitors are USB c monitors?

@Adamman125  the TB16 doesn't support DisplayPort MST on its outputs.  That's noted in its documentation.  So you wouldn't be able to run a daisy chain setup where Display #1 was connected to the TB16 and then Display #2 was connected to Display #1 (and ultimately to the dock through Display #1), but you could still connect each display independently to separate outputs on the dock using any combination of the "upstream" TB3/USB-C, DisplayPort, Mini-DisplayPort, and HDMI ports.  Note that with displays that have native USB-C inputs, I've noticed that some docking stations and systems don't always seem to work that way.  Dell for example has a KB article noting that the XPS 13 9350 doesn't send a video signal when connected via USB-C to certain Dell displays, and a friend of mine with a MacBook Pro found that the "upstream" USB-C/TB3 port on his Caldigit TS3+ dock didn't send a video signal when he used a USB-C cable to connect to his Dell USB-C display.  In both of those cases, however, using a USB-C to DisplayPort cable from that port to the display worked fine.  I'm not sure this issue would present itself with the TB16, but just fyi.

Also note that since the TB16 was released, Dell has replaced it with the WD19TB that you might want to consider instead.  However, depending on the resolution(s) of the displays you want to run, you might have some limitations around which combinations of outputs you can use to run both displays at their native resolution.  The WD19TB's manual breaks that down, but if you need some help sorting it out, let me know what dock you intend to use and what display resolution(s) you want to run and I'd be happy to give you some options.

Thanks for the quick response! But I don't think I was clear in my original post; I don't want to use a dock at all, I simply want to use the USBc/Thunderbolt port on the laptop, and then daisy chain.

@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?

@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.

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!

@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.

Thanks again for the great response. But I have a new concern, that is raised in this review from amazon:

https://smile.amazon.com/gp/customer-reviews/R3GIAGXWI0IMIP/ref=cm_cr_dp_d_rvw_ttl?ie=UTF8&ASIN=B07JQTNCGB

Essentially he says that:

"To daisy chain monitors, a protocol called "multi-stream transport" (MST) is used to drive the second one in the chain. USB-C does not have enough bandwidth to run two displays in 1440p with MST, unless you run USB-C in "alt-mode display port". This is essentially a USB-C to display port cable, and the connection essentially becomes a display port connection. That means you can't use USB-C for power or data, just for the display. It took me weeks of trying to figure out all the USB-C, alt mode display port, MST issues to figure out why my second display wasn't working. What I really needed was a thunderbolt 3 display, not a USB-C display - even with the same cable, they are not the same."

Is it true that, even if I rely on the barrel connector to power my laptop, using USB C means I wouldn't be able to use any of the USB 3.0 ports on either monitor as well??

Sorry to add yet another addendum, but I guess you can't edit...

I realize that getting a dock, the WD19TB you mentioned might solve this (is that true)? The issue with that is on the product page it does NOT specify that my computer, the XPS 15 9570, is compatible...