Got my proporta USB TurboCharger.
the micro usb plug that comes with it is too large to fit into the n900 (also too large for n96, so i guess its not standard).

it also comes with a plug for the previous nokia chargers, so i used it with the small power adapter that comes with the n900 and it charges ok*.

*though the adapter gets a bit hot and charging takes forever through this thing.

UPDATE:
i've contacted proporta, and they sent me a new connector head that works!!
*no need to short the data pins (http://talk.maemo.org/showthread.php...sb+charge+pins) the connector head already does it. so the retractable cable that comes with it can be used with any dumb charger.