I figure someone has probably already spotted this, and I haven’t really looked into the power supply situation for the mbSID much yet…but is this a possibly alternative to the C64 power supply?
You could get the 5V off the +12V rail via vregs, but @ 300mA that’s not gonna do much good. But since a 9VAC-11VAC wallwart is pretty much all you need, I don’t see what all the fuss is about anyways.