A friend worked on a blender. The wattage number was derived from the inrush current when first turned on.

I’m glad I don’t have that blender. :) (I’m the proud owner of a blender with a bona fide brushless motor. I don’t know specifically what type, but I suspect the inrush current is quite low. It also outputs considerably more power than most brushed motors can probably manage for any length of time.)

edit: The product blurb says it’s an induction motor. The nameplate says 1000W. It would be fairly straightforward to estimate the efficiency by blending a known amount of water and measuring the temperature change over some period of time.

To be fair, that might be the current draw in stall.

They are basically the same quantity - the motor doesn't care if the rotor is stopped because it's physically locked in place, or just because it was previously not running.

I don’t think so. Attempt the opposite experience: If you turn the motor, electricity comes out. So I don’t know what is the draw when stalling but I guess the draw must vary a lot even inside a north/south cycle.

In fact, the draw varies enough during the cycle that it’s a well known method in industrial ecology to put a condenser on a 60Hz motors when the supply is 50Hz. So there must be a visible cycle.

The magnetic behavior of the windings can depend on this, though. A good example would be a toroidal transformer, which tends to have a high inrush current, even if the output is open circuit.