I have bought my N900 from second hand with a charger Nokia AC-10E. But I have some doubts if this charger is original one.Can anybody tell me what is the difference between original and fake AC-10E chargers (which are probably very often selling as original ones). For example I saw these chargers with only one screw. Is it different version of AC-10E ?

And I noticed that when I am charging my N900 using charge21.sh script, charging current is not constant (950 mA), but depends on current used by the phone. Also when voltage of a battery is higher, charging current is lowering. Is it correct or is it symptom of fake charger, which can not give stable current?

The charging behaviour is exactly that way, by design. Enjoy your new-to-you N900 :-)

Thank you for your answer. Could you please describe it more precisely. And how to distinguish original form fake charger.

BTW, my I have my N900 for almost 2 years, but so far I didn't analyse process of charging.

DocScrutinizer (and others) made a study on this:

http://wiki.maemo.org/User:Joerg_rw/jrbme/

As for originality - I would say it's no big deal. As long as the charger can provide enough current and correct voltage (which yours clearly does), and has the short on D-/D+ pins (yours does too), then you're fine.

I would even bet most of the remaining N900 have not had the original charger treatment for a long time by now

Another battery analysis (not exactly charging, but may help):
http://talk.maemo.org/showthread.php?t=81477