How to improve power supply?

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.

Like many other electronic components; regulators generate noise. A number of ways to address that noise have been discussed and tried, by hobbyists and companies. ie: (http://www.edn.com/electronics-blogs/the-practicing-instrumentation-engineer/4422750/Simple-circuits-reduce-regulator-noise-floor) (http://www.diyaudio.com/forums/solid-state/1437-reducing-noise-voltage-regulators.html) (http://www.belleson.com/comparenewclassd.php) (http://www.belleson.com/compareburson.php) (http://www.ti.com/ww/en/analog/tps7a30/index.shtml?DCMP=hpa_pwr_tps7a30&HQS=Other+OT+tps7a30-bt2)

YES, Mr P: That silence reveals the truth of the saying, "You don't know what you've got, 'til it's gone!"

Try a couple sheets of Sorbothane, with the cord between. Be certain that the bolt(s), holding the x-former, remain(s) free floating(isolated from the chassis) as well. Good info: (http://www.sorbothane.com/standard_product_guide11.php)

Keep in mind, if using MuMetal sheet; If it has to be bent(to
any great degree), annealing in a hydrogen atmosphere is
recommended, to restore the grain structure/permeability.
MuMetal foil is also available, if you can arrange a way to
surround the transformer with it. The foil doesn't require
annealing, unless severely formed or heliarced. One source:
(http://www.lessemf.com/mag-shld.html)

I've use Sorbothane, in a number of applications. A great product. The bolt can contact the transformer, but needs to be isolated from the chassis(or vice versa). Nyloc nuts and flat washers are good for maintaining the position of your transformer, and keeping the nut on the bolt, without having to tighten them all the way down and transferring vibrations. ie: (http://en.wikipedia.org/wiki/Nyloc_nut)

Happy listening!