By using that cheap SCR "chopper" you have created a measurement problem for yourself. Since you have a non-sinusoidal waveform, you need a "true RMS" measurement scheme for BOTH voltage and current.
You can certainly find RMS conversion chips that will allow you to construct a circuit that accurately reports equivalent RMS voltage and current. But that is not a trivial thing you can throw together with an Arduino. The measurement of your "dirty" power has now become the primary project vs. a simple measurement task.
It seems unlikely that you can find any of those inexpensive digital voltage/current meters on Ebay that will read true RMS. Even if you could find one that is powered separately (so that it will measure down to zero).
If you want to use a cheap, noisy chopper SCR controller like that, then you must pay at the other end with RMS metering. There are reviews on YouTube for popular-price, commodity DMMs which have true RMS, and they are relatively inexpensive. For example you could start here with Dave Jones' Digital Multimeter Buying Guide for Beginners: https://youtu.be/gh1n_ELmpFI
If you are going to be experimenting with SCR choppers and mains power, then you need a couple of decent DMMs with true RMS anyway. And you would need at least one anyway in order to calibrate your Arduino circuit with the RMS chips.