I saw an inverter read 95V on my DMM AC range yet its power was adequate to spin a motor designed for 120VAC.
I am surprised.
Let´s say grid is 230V, 50Hz ...
This means it has +/- 325V peak, and 230V RMS.
The same I expect from a "modified sine": +/-325V peak and 230V RMS.
With this it is able to drive resistive loads (like incandescent lamps, heaters..) as well as switch type loads with rectifiers that charge capacitors
(lamps are operated at their expected power, capacitors are charged to their expected voltage.
So a square signal (steep edges) could be: 5ms @ 0V ... 5ms @+325V ... 5ms @ 0V ... 5ms @ -325V .... repeating
Many other waveforms are possible. In reality many "modified sine" are of trapezoid shape.
One reason for the above values could be that the DMM was no "true RMS". (Maybe using - inaccurate - "rectified average" method)
* Rectified average of a 230V RMS sine is 207V
* Rectified average of the "modified sine" above is 163V
Klaus