My inverter produces over 240V AC, will it fry my equipment
Aside from regulation, a modified sine wave inverter will likely give a somewhat higher voltage reading on a typical inexpensive RMS-modified average-reading multimeter than the RMS value. If you think about it, the sine wave is more "peaky" than a square-topped modified sine wave so the RMS value will be higher for the same average magnitude. 

What matters for switching power supplies is mostly the peak value anyway. 

If your charger brick is rated (say) 100~240VAC there will be an acceptable overvoltage outside of that range- 254VAC is within Europe specifications. If you are concerned an oscilloscope with an appropriate probe would answer the question definitively- peak should be less than about 360V.