Any charger for the more recent Nokia phone lines - N80i, N95, etc. - will work flawlessly for the N800.
I've used both an N80i and N95 charger as well as use my N95 car charger on my N800 just fine.
Matter of fact, on long trips the N95 will sit in it's Proclips auto mount doing GPS nav duties with TomTom while the lil' woman will be sitting in the passenger side web browsing on the tablet via tethered BT through the phone at the same time.
Works well.