Hello OP, before you get a proper response from the guru, I can share my experience for which I had tested on my own setup.  When you connect more than one power source, Dell XPS will accept the power from only one source.  In this case, the laptop will choose the Dell charger over the docking source. You can conduct a simple test for yourself.  With the laptop unplug from everything, power on your laptop and tap F12, select diagnostics and hit Esc key twice to cancel, select advance so you can see the current system with detail info.  You will find the battery and charger information.  Now, plug in the thunderbolt cable of your powered dock and take note of the reading, battery flow probably around 13.5 V,, charging maybe at 1.2 A.  Now, add the Dell charger to another port on your laptop.  You will see the charger switch from 65w to 130w but the status of current flow and charging rate are still the same. Test concluded.  Exit to shutdown and unplug your system.
Hello XPS Forum, I am a new Dell member with limited knowledge about accessory compatibility across brands and would appreciate your help.  I recently bought an XPS 17 9520 laptop (great machine!).  I also have a Lenovo Thunderbolt 3 Gen 2 docking station from my previous work, which comes equipped with 3 AC adapters: 65W, 135W, and 230W (I have always used the 135W adapter which worked perfectly with my previous Lenovo Thinkpad X1). Now, when I connect the Lenovo docking station to the Dell XPS 17, I get the Battery Power "Slow Charger" message with a corresponding hazard triangle by the battery icon - i.e. the Dell is not happy as the battery charges too slowly.  From my cursory research, I think the issue is that the Lenovo docking station with the 135W AC adapter only distributes about 65W to the Dell, which expects the full 130W to charge properly.  My workaround is to plug in both the official 130W Dell AC adapter + the Lenovo thunderbolt 3 connector.  This way I get full battery charging power plus use of the docking station. My question is, am I risking to send too much wattage to the Dell by having 2 power input sources, effectively 130W + 65W?  Will this adversely impact the battery life down the line?  I read somewhere that the thunderbolt 4 technology in the Dell ensures that only 1 power source comes through (the 130w), while the second one activates the docking station without sending additional (or excess) power through.  If that is true, then I am a happy camper. Thank you for your help in confirming either way and allowing me to enjoy my XPS 17 for years to come.  
XPS 17 9520 with Lenovo Thunderbolt 3 Gen 2 docking station