NOTHING, unless your Mac needs power to charge. if it does, it is supposed to select the BEST and ignore the other.
Anecdote suggests that if the FIRST is adequate, all others are ignored.
Your MacBook Pro uses ‘smart charging’ to charge in the optimum way, and only when necessary. Plugged in is Not necessarily actively charging. There is substantial hardware and software cooperating on battery and charging issues. Connected power sources simply 'offer' their charging ability, and the computer decides what to accept and when. Simply asserting a charging voltage against one of the interface(s) will NOT successfully charge your MacBook Pro.
Any external power supply that provides "USB Power Delivery" (including certain Docks and Displays) must negotiate over the USB cable using USB Power Delivery Protocol, and can not 'force itself' on your Mac. The Voltage and Current are delivered only after your Mac requests and the charger agrees to supply power under certain controlled conditions. The computer is in control of the entire process.