The PD breakout board for Pi5 - #27 by James46717 thread covers most of why you would use the official supply.
For me this is the important part from the Raspberry Pi documentation.
While USB-PD capable phone chargers advertise greater than 15W of power, virtually all of them achieve this by increasing the voltage instead of providing more current at +5V. If you are using a power supply that cannot provide 5A at +5V on first boot you will be warned by the operating system that the current draw to peripherals will be restricted to 600mA.
Regards
Jim
