Power amps and preamps are of course very different in their internal designs, regardless of whether they are from the same manufacturer or from different manufacturers.
They also draw very different amounts of current through their power cords, of course.
And in most cases they draw currents which fluctuate very differently as a function of the dynamics of the music, fluctuating essentially not at all in the case of preamps, while fluctuating widely in the case of power amps operating in class AB or class D. Consequently they may have very different sensitivity to the bandwidth of the power cord.
They have very different internal voltage regulation, none at all in the output stages of most power amps; very tight voltage regulation in the case of most preamps. Consequently they have very different sensitivity to voltage drops that may occur in the power cord.
Power amps can generate significant amounts of high frequency noise that can be fed back into the power cord and affect other parts of the system, to a greater or lesser degree depending on the shielding, bandwidth, capacitance and other characteristics of the power cord. Preamps generally do not do that, and even if they do (perhaps due to digital circuitry they may contain) the noise would have very different technical characteristics than the noise generated by a power amp.
Given all of those differences, from a technical standpoint it can be expected that preamps and power amps will react very differently to power cord characteristics. And therefore cords from the same manufacturer would seem to be no more likely to be an optimal combination than cords from different manufacturers.
IMO. Regards,
-- Al
