None of the newer USB C PD rev 2.0/3.0 have 12v rails only rev1.0 devices have.
5, 9, 15, 20v will be negotiated by the device.
There is absolutely no advantage to use a usb-c PD device unless you are sharing it amongst various devices that may change in voltage input range.
None at all if its going to be static for powering a RockPi4 unless you like that type of “wall charger”.
Also the regulation and efficiency on a computer power supply is likely to be much better and a gold (87 -90% efficiency) rated up to about 600 watt can be got for the price of the PSU you posted.