I finally came up with a good solution that I am quite happy with. My 2 x Dell U2419H monitors have both DP and HDMI inputs and it turns out I can easily switch between the video inputs through the monitor menus. So I connected my desktop XPS 8930 to the DP inputs (daisy chained using MTS), and then connected the Dell laptop via an "Alt Mode" supported USB-C port to a dual HDMI splitter which connects to the HDMI inputs on the monitors. I can then switch between either laptop video inputs or desktop video inputs easily (or even have the desktop on one monitor and the laptop on the other if I want to, and if I keep the laptop screen open, I can actually have 3 active screens for the laptop). That just leaves the mouse and keyboard, which I ended up using some free Microsoft software called "Mouse Without Borders". You hook them together via a network/Internet connection and it lets you control multiple computers with the same mouse/keyboard and it simply moves the mouse from the desktop screen to the laptop screen like they are a part of the same system (even works across VPN). Simple and elegant and pretty tidy solution. So all I needed to purchase was the USB-C to dual HDMI splitter and an extra HDMI cable. Ended up being much cheaper and more affordable that the equivalent KVM solution I was considering, so in the end not being able to connect my desktop via DP Alt Mode saved me some money!  Thanks again for the input.
Subject says it all really ... I have an XPS 8930 and I am trying to determine if it's DP Alt Mode compatible before I go shopping for a KVM switch box and cables. Basically my goal is to connect this XPS 8930 desktop and a Precision 5550 laptop to a KVM switch box via USB-C cables which will then connect to my dual U2419H monitors via a DP chain using DP Multi-Stream Transport (which yes the monitors support). All the documentation I can find says the back USB-C port on the desktop is USB 3.1 2nd Gen, but mentions nothing about DP Alt Mode, either yay or nay! I would have presumed that simply means it doesn't support it, but I noticed the Precision 5550 laptop also labels it's 3 x USB-C ports as USB 3.1 2nd Gen (although they do mention DisplayPort and Thunderbolt in the specs). Would be good if anyone can confirm if the XPS 8930 USB-C ports definitely do or dont support DisplayPort Alt Mode. If the answer turns out to be no it doesn't support it, I would welcome peoples recommendations for KVM switch products to connect my XPS 8930 desktop and Precision 5550 laptop to my 2 x U2419H monitors, USB keyboard and mouse. Each machine will have it's own direct ethernet connected, and I am expecting audio should already work through the DP cables. Thanks all.
Does either of the USB-C ports on XPS 8930 support DisplayPort Alt Mode?