Plug in a volt meter and tell us what you see. With TRUE SINE Inverter generators you may or may not be able to use a Kill-a-Watt (there is debate on this I have a Kill-a-watt plugged into a true-sine-wave inverter powered line no problems. others have reported problems)
You can also use an analog volt meter I have 2 of those that plug in too one was free (won a drawing) the other I paid for (Too much) at Camping world.
The one I like best is by MFJ enterprises and is a plug in meter with pass through (that's my favorite analog) you can google MFJ plug in voltmeter.