I am trying to find if usb audio class 2 specify a max power on the bus, for some reason I can quickly find the spec, but I certainly wouldn't feed 100 W next to a non error corrected stream of Data, there is no way it could comply, this spec should be somewhere tough. In any case, power delivery thing don't apply, it's if you don't do anything else than supply power, but even then, doesn't apply to charging your phone neither, I think a computer can supply like half an amp to a USB device, but I could be wrong.
UAC2 is more or less on top of the base USB spec. 5V, max 500ma for 1 and 2, max 900ma for 3.
Power delivery allows the source and sink to negotiate voltage and current requirements. IIRC the spec allows for anything between 5 and 20 volts at up to 5 amps. The interface chips on each end are powered by the base 5V so they can talk to each other.
The sink specifies a voltage range it can accept and the maximum power it will draw. If the source can supply something within that range it will go ahead and do it, and the sink device will power up. If not then it just doesn't work, but doesn't break anything either.
The problem is that the source device may not have enough power or support a specific voltage. The sink can request any arbitrary voltage between 5 and 20, but that doesn't mean the source and regulate at that specific voltage. It's something
I ran into when I was working on this little project. My USB3C PD powerback would support more voltages than an AC charger I had. The charger only supports 5, 9, 15, and 20 volts output while my powerbank also supports 12V out, which is a much more common voltage for desktop equipment with external power supplies.
A designer could always increase compatibility by accepting any voltage above the minimum required and regulating it down, but that will increase cost by requiring over-speced components and more robust thermal design.
Even though the ADI-2 DAC's manual says you can run it at anything between 9.5 and 15VDC I would prefer to run it at the standard 12 (per its included supply) just to keep the heat down.