Ptss, how do you know it is inadequate? Most likely it is linear power supply followed by voltage regulators. AFAIK nothing changed in design or available regulators since mid 90s. There are few areas that might bring improvement. It might be possible to replace power supply caps with better ones, replace rectifier with one that has soft recovery diodes, add high frequency filtration of input voltage - either external (power conditioner) or internal (metal box modules or power socket with filtration). It is also possible that your pre has fine power supply but something else deficient. Why not to sell it the way it is?
