Sano,
if I remember well from a smileAOTworks post, there is a sweet spot for the electric field : too much will destroy the alignments of molecules chains, and cancel the viscosity reduction.
So how do you know if it is a question of not enough power, rather than a question of reaching the sweet spot which in turn is depending on flow, temperature, type of oil etc.... much more complex than what you say, and which can explain the delay in designing the right power supply.