Simple mod for RaspberryPi and HifiBerry DAC / Digi - plus various others ;-)
''but the Gnd may be needed as may the Screen connection - it seems to depend on how the computer recognises that the USB port is active''
yes very good point.
Sometimes the 0V handshake is needed between PC and device.
But IMHO this is an area well worth having a play with different PSU's.
I used a TP 5V Shunt to feed my WaveIO but the heat at 450mv was a little too much in the end so I switched back to a linear.
The shunt sounded nice.