AFAIK amp meter can't properly measure protected power supplies based on AC/DC transformation, cause it tries to pull as much current as it can = trigger power supply protection mechanism. On "smart" fuses it will only limit current from power supply or at worst shut power supply down for few seconds/minutes/until re-plugged to wall socket. Dumb fuses will just burn out, replacement needed. Unfused units will just start to fry. So, unless dr_frost_dk implemented some unusual measurement method, I don't recommend trying this, nor it can show real current. Nevertheless, it's true that N900 limit current (and almost every electronic device do) so it's even better if You have more powerful power supply. Thanks to that, N900 can pull as much as he/she ( ) want, and power supply isn't stressed.
There's no problem in measuring current. What you describe is short circuiting the powersupply to measure how many amps it will provide, which is a different topic.