Is the usb port directly attached to the mobo? Maybe that could help
I once had an amp (not a dac) that was powered via usb. When the power was supplied by the mobo usb port it sounded terrible, but when powered with a phone charger it sounded perfect, but the amp was too tiny for what I wanted. I got a dac and amp now that each get their power from the wall, and its been great ever since.
I could be wrong, but see if you can buy a usb cable that splits power and data, and plug the power side into a decent separate usb power supply separate from he computer.