How to improve power supply?

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?

The power transformer. Look into Plitron transformers. This update could be HUGE in clarity and dynamics.

If your power supply does have regulators, replace them with Bellesons, which are much quieter(http://belleson.com/download/Superpower_datasheet.pdf). Replace the rectifiers, or bridge, with with either HEXFREDs or Schottky diodes. Parts Connexion offers small PC boards, for building your own bridge with discrete diodes(if needed). Your filter capacitors could probably use a freshening up. Why not increase the capacitance, and pick up some dynamics? Keep that increase to 20% or less.

Hi K.
I know it's deficient because of the "inordinate" gains I obtain from using a 'combination' of ac power isolation & conditioning devices bought to enhance my listening. I am using -and need to use- an Equitech 2Q balanced transformer, MIT AC2 & AC1 reference power cords, and MIT Z Stabilizers--all to excellent effect. Spectral advertised the DMC 20 separate power supply as very effective - and it is the size of the preamp control unit; however I don't find that it is good in the real world (knowing nothing of lab tests/performance). Perhaps it's excellence is in it's ability to allow me to hear the gains by my power products? But, I expected it to provide quite clear power on it's own. Do I expect too much?

Thanks Ja. As you see above I am using the oversize 2Q Equitech unit to provide balanced power. I appreciate your PLITRON suggestion however EQUITECH products are being used by NASA and Ames Research Centre so the quality must be there. Also, I note BETA Transformer Technology Corporation is providing the same to NASA and Military.