How is the output voltage adjusted on this schematic?
In normal operation, an external circuit would be connected to the CTL pin to handle negotiation. It will add a resistance to ground to increase the voltage.
An example of such a device is the TPS25740.
You can just add a resistance where R43 (DNP) is shown in order to statically change the output voltage.
The ATL431 will have 2.5V from pin 2 to pin 3 when it is in regulation, so with CTL open you get 5.0V out.
With CTL shorted to ground you get 20.06V out, because of the internal 24.9K resistor. For intermediate voltages just calculate the required shunt resistance and subtract 24.9K to get the required external resistor.

If you want 15.0V then the current through the top 150K resistor R41 is (15-2.5)/150K= 83.33uA. So the bottom resistors must combine R45||(R42+R43)
to represent 30.0K.
Which means that R42 + R43 must add up to 37.5K, so you would install a 12.6K resistor for R43.



simulate this circuit &ndash; Schematic created using CircuitLab