The electrical activities inside a PC and the quality of the PSU itself might send all kind of stray signals over the power lines of the USB into the DAC.
You can get rid of this noise by powering the USB receiver of a DAC with a separate very quiet PSU.


AQVOX USB Low-Noise Linear Power Supply EUR 98,-

iFI Audio iUSB € 225.00



Claims to be quieter than a battery.


Source: Why a USB Power Supply?


iFi Gemini Dual-Headed USB cable

Gemini Cable 0.5 meter – € 135
Gemini Cable 1.5 meter – € 225


You have that ultra-quiet USB PSU and you still need a cable splitting signal and power?