The power output of a generator is generally not a voltage problem, but a frequency problem.
If the generator does not output exactly 50HEZ alternating current, abnormal operation may occur. First, check if the generator is equipped with a voltmeter and frequency meter.
In general, a lower frequency is more likely to occur. Air conditioning compressors are inductive loads. Decreasing the frequency will increase the current. Generally this cannot be measured because the increase is the DC component. If the frequency is very low, it is easy for the motor to overheat and burn the motor windings. This increase in current cannot be converted to power and will also reduce the power output.