Does it really matter? I would be more interested in the peak voltage. Take a diode and run it into 10uF or more. Should be 140V. For mosy electronics it will not matter. For motors more dead time (lower apparent voltage) it will ne a plus.
So-called 'modified' sine wave, typical for old or cheap&nasty inverters. Its used to deliver equivalent power into a resistive load while still maintaining the same peak voltage for electronic devices that full-wave rectify the mains.
Cheap meters that aren't true RMS usually rectify the input on AC ranges and are scaled to read 11% high compared to DC because, for a pure sine input, the average voltage is 0.637 of the peak, but the RMS voltage is 0.707 of the peak. Feed them a square wave and they read 11% high. However if you feed them a 'modified' sine with 60% on time in each half cycle, they will read about 2/3 the correct voltage.
There are other more sophisticated waveforms that more closely approximate a sine wave but still underread on a cheap average reading meter.
I'm partial to the 2000W inverters HF used to sell for $129. I should disclose that all (6) the ones I bought were purchased as defective.
The manufacturer of the inverter does not know or refuses to say it is a cheap squarewave inverter that was used 30 years ago in third world countries. Since it has a squarewave then its peak voltage is the same as the RMS voltage of a mains sinewave so it does not blow up an incandescent light bulb or a heater. But a cheap meter measures its peak voltage then reduces it to the RMS voltage of a sinewave so it reads the voltage wrong.
Many modern electronic products do not work from a squarewave inverter because they rely on the 41% higher peak voltage of a sinewave.
The manufacturer of the inverter does not know or refuses to say it is a cheap squarewave inverter that was used 30 years ago in third world countries. Since it has a squarewave then its peak voltage is the same as the RMS voltage of a mains sinewave so it does not blow up an incandescent light bulb or a heater. But a cheap meter measures its peak voltage then reduces it to the RMS voltage of a sinewave so it reads the voltage wrong.
Many modern electronic products do not work from a squarewave inverter because they rely on the 41% higher peak voltage of a sinewave.
i suppose they use counterfeit 2n3055 transistors too eh?
btw, modern equipment should not care about the voltage or frequency.
A SMPS designed for 70V to 240VAC input does not care if much if its input is a squarewave with a low peak voltage. But a power supply with a low frequency transformer, a rectifier and a filter capacitor does care.
Square wave inverters have been obsolete for years, ever since the 'modified' sine inverter became common.
Older SMPSUs frequently had a much narrower input voltage range, and often required manual switching between 115V and 230V input. It was possible to design a fully autoranging PSU, but that resulted less efficient magnetics, and needed a higher current switching transistor, which increased cost. So back in the days that 'modified' sine was popular it was important for the peak voltage to be compatible.