If you plug that power supply into almost any USB C device, chances are extremely high that the magic smoke will be released. Is risking a $400+ phone in a moment of inattention worth the risk?
And why do you need to buy new adapters "for stuff"? Do you have more than one of these non-compliant adapters?
Not if they are PD compliant. Measurement error on your part?
The voltages put out depend on the wattage of the charger. 20 volts --> 60 watts. If the charger doesn't put out 60 watts, it will not supply 20 volts.
Indeed there is,
depending on the rated wattage. It's really not that difficult to understand.
It's a standard. To say a power supply is PD compliant, it must meet the standard.
Your RANT about 12 volt operation was already addressed by
rjenkinsgb.