Can a better power cable make a difference if NOT plugged directly into an outlet?

@thyname   It's interesting he mentions "galvanically isolated" for DAC's to "clean up  and isolate noise", since doing so introduces a transformer or capacitor in the USB chain, which can change the phase of the signal.  But it hardly matters because this is the analog side of the signal, which is not used directly by the DAC. 

Finally, all but the cheapest USB hubs are already "galvanically isolated" to ensure an accurate clock signal on the downstream USB ports, so I'm not sure where's he's going with the entire message.

@thyname  "or get an engineering degree"

Already done.

"It’s a bit of stretch to say all USB hubs are already galvanically isolated"

I didn't say all,   But no doubt some manufacturers will put their name on an average USB hub, put a nicer case on it and sell it for a lot of money to convince you it has some advantage over the ones you can buy for $30.