I had to go back and remind myself what i read back when i last looked at Pis for audio. I've had other pressing issues int he intervening 9 months. From my perusal of the (sparse) documentation and the schematic it seems that they have separated the USB onto it sown controller and stopped loading the processor with some of the Ethernet duties- both of which will reduce some of the noise, to the degree that noise is proportional to workload.
As to the supply - if you mean the EXTERNAL supply, that’s where you need to spend some time or money. I built a well regulated and filtered , 3.5A linear supply. It ought to quiet things, and listening tests (vs the $7 standard issue cana-whatever unit) strongly supports this presumption. I can’t speak to mot commercial supplies, having never used them. Well, one exception - i had an ALLO DAC/Pi based bridge/Shanti to evaluate and study for a while and it was an impressive power supply for the price, I thought. It costs something under $200 and if i recall also supports both dirty and clean 5V outputs.
I also isolate the USB of the DAC following (if using the one i half-built) and the commercial ones has built in isolation, quite good from what i could see visually (an SMT transformer)