Charging of Macbook Pro 15 inch Touch Bar

Re:

“ ... That's what I recall finding from an authoritative Apple source in 2017 when I was researching for my current MBP ...

... but I can't find it now to save my life. :-( ... “

Well I finally “stumbled across” my original single-charging source reference.

https://support.apple.com/en-us/HT207097

Cheers.

Your Mac will charge from only one source, and it will pick the best one. "If you do plug in more than one AC adapter, your Mac will automatically select the single best-suited power source and charge from it."

From Apple: Charge your MacBook Pro with Thunderbolt 3

The laptop will pick one charging source ... probably the 1st one it sees.

And FWIW, I've been running my own 2017 MacBook Pro 15" Touch Bar all day on an 18 watt Apple USB-C charger and it's the State of Charge (SoC) has been climbing slowly all day.

I've been running basic office apps and browsing / e-mailing via WiFi all day.

Obviously if I'd been doing more intensive computational / graphics tasks, 18W couldn't have kept up ...

... just including it here to show that there's a wide range of actual power demand far lower than the "nominal full load" spec'd.

Re: "... So they would only use one source? ..."

That's what I recall finding from an authoritative Apple source in 2017 when I was researching for my current MBP ...

... but I can't find it now to save my life. :-(

Hopefully someone more knowledgeable and with a cite might chime-in.