How to improve power supply?

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.

09-17-14: Ptss
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.

this is a totally wrong assumption on your part. Even if you improved your in-chassis power supply, you would still need the AC isolation & the Equitech. Almost all the power & pre power supplies are unregulated so they are quite sensitive to the grunge on the AC power coming out of the wall socket.
The AC isolation & the Equitech unit is cleaning up the AC power coming into your electronics & it will still need to be in place after you upgrade your pre & power supplies.

Now, your power supply caps probably need to be replaced as correctly suggested by Rodman99999 simply due to the electrolytic dielectric material drying up over a period of 20 years. You could also gain by using HEXFRED rectifier diodes, I agree with this.
But you will still need the AC isolation & Equitech after all these upgrades.
IMO you could get rid of the AC isolation & Equitech if you had a regulated power supply (like a SMPS used in many class-D amps). A regulated power supply will maintain regulation over a wide range with very little output ripple & will also have good load regulation (i.e. minimal output voltage changes when the load current suddenly changes. Sudden changes in load current are expected as a normal when listening to music which is quick moving signal).