Measuring 0-250V and 10A (AC) with arduino
Most cheap voltmeters and ammeters will display entirely the wrong numbers when dealing with non-sine outputs like that will produce. You need a true RMS meter.

I would suggest just dropping the arduino, and using something like this.

If it needs to run at low voltages, a meter like this with a separate supply will work - but ouch on the price.

I'd try getting the first one - it might work to lower TRMS voltages if there's still the high peaks; it depends on what they're doing in the power supply. You might also be able to separate the voltage input from the power supply.