DisplayPort monitor for XPS 9560

I ended up buying this: https://www.amazon.com/Displayport-QGeeM-Thunderbolt-Compatible-MacBook/dp/B07V2ZM8DF/ref=sr_1_5?dchild=1&keywords=usb-c+to+displayport&qid=1587679488&s=electronics&sr=1-5

Hopefully it's correct. Thanks so much for your help!

@crmccar  there's a known issue with the USB-C ports of the XPS 13 9350 and XPS 15 9550, but that only comes into play when using a regular USB-C cable to connect to certain Dell USB-C displays.  And there's a known issue with the XPS 15 9570's HDMI output whereby it doesn't work with DVI displays.  But none of that applies to your system or overall display scenario.

You don't need a Thunderbolt cable, and in fact if your display doesn't have a USB-C connector input (does it?), then a Thunderbolt cable would be completely useless to you.  But even if your display does have a USB-C port, and therefore a Thunderbolt cable would be usable, it would still be unnecessary.  The vast majority of displays with USB-C connector inputs just use regular USB-C.  There are very few displays that actually use native Thunderbolt.  Apple has an old display that used Thunderbolt 2, and the only Thunderbolt 3 display I know of is LG's SuperFine 5K display (5120x2880) -- and then Apple has a new 6K XDR display coming out that will use that as well.  But the XPS 15 systems wouldn't even support those 5K or 6K resolutions anyway due to GPU limitations.

A USB-C to DisplayPort cable would allow you to run up to 4K 60 Hz.  The only reason you'd need Thunderbolt would be if you wanted to run two of those from that same port, in which case you WOULD need the extra bandwidth that Thunderbolt offered, and you'd have to use something like a Thunderbolt 3 to Dual DisplayPort adapter or a full Thunderbolt dock like the WD19TB to achieve that.

Yes, any USB-C to DisplayPort cable will do.  The XPS 15 only supports DisplayPort 1.2 over USB-C, which was the first DisplayPort revision that was supported on USB-C, so every USB-C to DP cable will support that.  And a 1080p display only requires about 25% of the bandwidth available over DP 1.2 anyway.

@crmccar  should be fine!  The note about "Thunderbolt compatible" just means it works on systems that have Thunderbolt-capable USB-C ports as opposed to just USB-C ports that support DisplayPort Alt Mode.  The cable won't work any BETTER on a Thunderbolt port, and all USB-C to DP cables are inherently Thunderbolt-compatible, but some manufacturers include that compatibility note purely to avoid having customers constantly ask, "My system has Thunderbolt -- will this cable work?" -- or worse, losing sales entirely from prospective customers who just assumed that it wouldn't work without bothering to ask, or perhaps bought the same type of cable from some OTHER vendor whose product page specifically said "Thunderbolt compatible" to reassure them -- even though that other vendor didn't have to do anything special at all to make their cable Thunderbolt compatible.

It would be a bit like selling a USB cable that said "Works with printers".  That wouldn't mean there was anything special about that particular USB cable -- but I guarantee you that if some USB cable vendor started doing that, other competing vendors would be forced to update their own product pages to say that as well, just to avoid confusion or lost sales from customers who would now become confused/concerned about USB cables that didn't explicitly specify printer compatibility.

@Cappuccetto  The issue I’m referring to has affected every Dell USB-C display I’ve seen tested with those systems, including displays made years after that article was published. Or to say it another way, I have never seen a report of somebody connecting one of those systems with a regular USB-C cable to a Dell USB-C display and seen them report success. So unfortunately I would not expect this to get fixed.

But since the 9550 is designed for a 130W power source, which is more than the U2421E provides, relying on a USB-C connection fir a single cable solution isn’t ideal anyway. You’ll want to connect power separately. So at that point the only additional workaround you’ll need is to connect USB data separately from video. Basically you need to do this:

• Use a USB-C to DisplayPort cable for video. This will work with the 9550’s USB-C port even though the regular USB-C cable method doesn’t. This will get you video.
• Use the USB-C to USB-A cable that came with the display to get USB data connectivity if you want to use the USB and/or Ethernet ports built into the display. (Connect the display’s USB-C input to a USB-A port on the XPS.) If the cable that came with the display isn’t long enough for you, make sure you get another one that supports USB 3.x Gen 1. Some C to A cables only support USB 2.0.
• Keep the system’s power adapter connected to the barrel-style connector on the XPS.