An AC current source?
Isn't it just
Apparent/Complex Power: S = (I^2)*Z = (I^2)(R + jX)
Real Power: P = Real(S) = S*cos(theta)
Reactive Power Q = Imaginary(S) = S * sin(theta)
Where "I" is a phasor and theta is the phase angle of the phasor. Can't seem to find a way to make the angle character here. But I suppose if "I" is just set to zero degrees and all other phase angles in the circuit are referenced off that, then you can just use treat it like a magnitude which gives you:
Real Power: P = Real(S) = magnitude(S)*cos(theta) = S*cos(0)= (I^2)*R
Reactive Power Q = Imaginary(S) = magnitude(S) * sin(theta) = S * sin(0) = (I^2)*X
EDIT: I'm a bit wary though since something like (I^2)*R is only valid for AC if "I" is RMS, but in here it's obviously the peak value/magnitude of the phasor. At the same time though it feels wrong to just throw in a 0.707 fudge factor...unless the magnitude of the phasor is already the RMS value... but that seems really weird to me since it does not seem physically representative to have a rotating RMS line. But maybe we really do just throw in a 0.707 fudge factor and the phasor magnitude represents the RMS just so we can use the conventional equations. I'm pretty damn sure there needs to be 0.707 in there, I just don't know how to work my way into introducing it in other than saying "it has to be there cuz RMS".
Okay, now I have the same question too lol.