Usually, the 5V power rail of raspberry pi is generated from a DC/DC converter, which always means pool ripple rejection. To overcome this , the power rail of the HAT has been build with two levels of active regulation, which brings extremely good PSRR performance in full band under full load, so the power supply of the DAC would be perfectly clean.
This processing unit is placed at the backend of the power input switch, so both RPi power and external power sources are valid.
Laboratory test data
When VDD in full load, PSRR = 111.61dB
When VDD in lite load, PSRR = 119.78dB
The test data is from wisdPi laboratory and is for reference only.