I was posting the same question on a German KTM site, the result was more or less:
2003 KTM 640 Adenture electrics:
generator output: 200W
The cockpit 12V plug has a 5A fuse, thus maximum power is 60W.
Thus as long as you can get a power supply with less then 60W you should be fine to charge a notebook. Power converter to 110V/230V might work as well (most run at 90% effectivity).
But in the meantime, I basically gave up the idea of carrying around a notbook.
Vibrations, dust, extra weight and this fancy small sub-notebooks are just tooo expensive...