Confirming that nokia charger (original) doesn't produce DC current (not clean DC at least).
I connected headphones and hear high pitched sound, while DC should be silent and cllick on connection only. Can't say much more without an osciloscope but I'll refrain from using my usb chagher. It either never managed to fully charge or just messed up tablet's charger status.
Either way I never saw "Fully charged" mesage even after leaving to chaarge over night in off mode (but tabllet worked for the whole day after).