USB contains 2 wires for digital signal and 2 wires for "USB Power". This is just 5V DC and it's driven from the computer/laptop (which is basically the same or worse than a wal-wart switching power supply).
Also agree completley with timlub. You can just compare op amp specs and expect it to tell you exactly how good a DAC/preamp is.
Also agree completley with timlub. You can just compare op amp specs and expect it to tell you exactly how good a DAC/preamp is.