Mine doesn't work for the N900, giving all the signs of a USB device wanting more power than the power source was willing to give. (Plug in, orange light blinks for a while, ghost Nokia logo shows on screen, and then a few seconds later a sound that means charger disconnected.) This story was the same with the N900 running, and turned off. The DC-11 was fully charged, and I tried multiple times with cables laid various ways to guard against any physical movement.
I'd say the DC-11 is not compatible with the N900, despite the theoretical match.