Well, if you’re measuring it correctly you’ll measure no more than 50mv overall. Unfortunately, it is a very difficult measurement to properly make and most people don’t have that ability.
Even on a Fluke it’s typically wrong. What needs to happen is the meter has to be on the same scale as the full output of the AC peak voltage (which is about 180 volts on a 120 volt unit). Problem is, when most meters are at their 200 volt scale
their low level accuracy is pretty bad for low level signals.
There’s a whole complicated engineering procedure we perform to test all these (and that procedure takes place on every Power Plant we ship).
Trust us. With 900mv in you’re Power Plant isn’t giving you more than 50mv output.