Doesn´t sound like the power supply. More like it´s picking up noise from somewhere. Here´s a couple of thing that could help:
- Avoid using very long cables
- Use balanced cables
- Use quality cables
- Try not to have to many cables to close together
Here´s a link to the hum from my SH-101 to give you an idea of how hum from a shitty power supply sounds. This hum is only pressent when i´m using the power supply (there´s no hum when used with batteries):
http://hjem.get2net.dk/revolution/hum.mp3