Non thermal plasma can be considered as a capacitor in parallel with resistance, then the current is the contribution of conductive current and displacement current. The dissipated power can be estimated from the energy of the capacitor.

Physically, the power consumption traduce the process of pre-breakdown or breakdown without arc creating. So, it depends on the electrical field withing the discharge Ed and its temperature Td. But Ed have more effect then Td because the different ionization phenomena.

Dr. A. Slama

You can use lissajous figure (Q-V curve) or by multiplying  the discharge current by the discharge voltage.

Dr. Kamal

You can use Manley’s equation that shows the rule of power consumption during plasma discharge.   You may check;

1- Non-Thermal Plasma Techniques for Pollution Control: Part B: Electron Beam ...

edited by Bernie M. Penetrante, Shirley E. Schultheis, Page 273

https://books.google.com.sa/books?id=1FroCAAAQBAJ&pg=PA394&lpg=PA394&dq=Manley%E2%80%99s+equation&source=bl&ots=GYF7I_DdUB&sig=Rv64mwCgjua08HvSLZtVRJEqz4g&hl=en&sa=X&redir_esc=y#v=onepage&q=Manley%E2%80%99s%20equation&f=false

2- http://www.scielo.br/scielo.php?pid=S0103-97332004000800047&script=sci_arttext

The general ruler calculating the power furnished to the plasma (per unit volume) by a generator is always \vec{J}\vect{E} if you can estimate the electric field. This expression is always valid. If you are making simulations these quantities are easily available. From experiments, I guess it is more difficult to measure J and E. In some configurations, i.e. flat plates, discharges, it is equal to I*V. I do not know if this expression could be generalized. I suppose so. But It should be demonstrated considering that J=dI/dS (S discharge section),  the flux of J over a closed surface is zer, and E=grad(V).