Plasma is to push 12v to 16v elec power. However, there are some sensors in between and cut by ECU setting before goes into spark plugs. For exampls, the stock car is running 70% elec power, with plasma push in, it may max a little more about 80% in total. For horsepower, I would say only 1hp increase maximum.
For Pivot VS (Voltage stabiliser), it act different way with Plasma of which it stores some elec power beside your stock battery, stable the elec current a little bit and hence longer the life span of the battery. For light mod cars, pivot VS is more than enough, for those who like heavy mod or heavy ICE kaki, you need bigger VS and higher end product such as HotInazma, Guangdau, Bellon, D1 Spec etc etc.
I hope this may help. Cheers.