Power warning with USB-C and ac adapter

I appreciate the response, but you missed the point of the question entirely.   I am charging with the AC Adapter.   I plug in my dock (AC Adapter is still plugged directly to computer).  I then get the power warning because my dock is ALSO sending power to the laptop (so 2 power sources at that point).  My question is, even though I get the warning, I want to know if it is still charging from the correctly sized AC Adapter and NOT the dock's 100W usb-c powersource.

My system is an XPS 15 9570.

No one can give you a definitive answer without knowing the system model you have -- but if it's an XPS 15 or 17 that has an nVidia or AMD GPU, 100W is not going to be sufficient.  These generally ship with 130 or 180W power adapters - while you can run them on USB-C, they will not run at full speed, nor will the battery charge as fast as with the correct AC adapter.

Excellent...thank you.  That is what I was hoping for / assumed.  I am not using a Dell dock, I am using a Plugable dock.   Do you know of any way to tell what source is being used?

In most cases, the system will start charging from whichever you've plugged in first.  Plug in the AC adapter and you should not see the error.  Then plug in the docking station.  The system should charge from the barrel connector rather than USB-C.

You have not mentioned whether you're using a Dell docking station, but with one that's how it should work;  with a dock from any other manufacturer, results can vary.