I have plenty of examples of new gear that has only usb power, usb power but can run on batteries, or mixed usb power and common Dc transformer but lots of noise humz anyway.
Korg NTS-1 runs only by usb connection. No batteries. Noise is terrible when used in a mix it's almost ubereable. I could only think of making a fake usb-battery pack just to run the Nts-1...
OP-1: Only usb power, but execcionally low noise.
All of Roland Boutiques, when usb connected, have noise. Unplug usb and run on dummy batteries and you are set, but lose the usb power of connecting to your Mac/Pc..
My other solutions are:
Audio filters, which thin the sound, but the get a lot of the nise off.
Ground the Device in some ways.
Use ferrite on cables I run either for Usb, and for Audio.
It doesnt' matter if I use a standalone High quality 220-5v usb power brick, or a high quality isolated out usb hub, or a low quality usb hub.
Noise is always there.
A fun video on the matter. And why it does matter.