If the car charger works then I would say it is most likely your wall charger that is at fault.

When charging from a dumb charger the N900 expects the data pins to be shorted (i.e. connected together), not all USB chargers do this, if the Blackberry charger doesn't do that, it would explain why it doesn't work for your N900. Maybe try charging your wife's Blackberry from your N900 charger, if it does charge then you can rule out it being a problem with the charger.