Hi
Average power is defined as
Pavg = (1/T) * integ(v(t)i(t)) dt (limits: tstart - tstart +T).
Since the supply voltage is constant, aveage power in a ganeral voltage supply
with voltage Vdc is calculated using the definition:
Pavg = Vdc * (1/T) * integ(i(t)) dt (limits: tstart - tstart + T) = Vdc * Iavg
i.e supply voltage times the average current. The rms value of the current
is however defined as:
Irms = sqrt((1/T) * integ(i(t)^2) dt (limits: tstart - tstart +T))
and is not the same as Iavg therefore multiplying by Irms doesn't give correct
result. rms values can however be used if both v(t) and i(t) are the same
type of signals or same types of signals differing by a constant.
Furthermore if you are certain that the same current flows through both
supplies then you can calculate Iavg (I think that there is a function in the
calculator to calculate average values of signals) and then multiply by dual supply.
otherwise the safest is to calculate the power in both supplies separately and add them.
BR