USB C Power Output On MBP

The issue may not be what your MacBook Pro is "capable of" as much as "willing to supply".

Is your MacBook Pro connected to its power adapter as you are trying to charge these other devices?

This third-party article suggests MacBook Pro supplies nominal 5 Volt power readily, but NOT at the maximum possible 3 Amps/15 Watts:

The USB-C ports on the MacBook Pro models also deliver 10 watts (5.2V x 2.1A, below 2100mA when adding Extra Operating Current to the Required Current) to any directly connected iOS device, so you can charge your iPhone quickly that way as well.

from:

https://appleinsider.com/articles/16/11/16/everything-you-need-to-know-about-usb-c-thunderbolt-3-on-apples-new-macbook-pro

The MacBook Pro supplies near the maximum the iPhone needs to charge itself at maximum speed. That article also notes that the 5 Watt default iPhone adapter provides less than the iPhone would be happy to draw, if its power adapter were capable of more.

EDIT: fixed some spelling errors and specs

That partly depends on the device attached.

Regular old USB devices can get 5V power up to as much as 1.5 Amps just by connecting to it. Newer devices may demand as much as 3 Amps that way. To get higher Voltages and higher Amperage, they need to use the USB-C power protocol to negotiate with the MacBook Pro for more. That is why USB power delivery cables for higher amounts include USB-2 data lines as well.

https://en.wikipedia.org/wiki/USB_hardware#PD

¿What are you connecting, and what does it need to get from the MacBook Pro?.