How to improve power supply?

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)

Thanks Rod, that makes sense. So basically I take it there should be 'isolation' material as a "washer" between the afixing bolt head and transformer surface as well as under the transformer.
I am going to check the torque required to loosen the bolt, which will be more than it needs to be retightened. Thanks for the SORBOTHANE idea. Coincidently I've read a bit about it lately and it sound good to me. If it's good enough for NASA and the Liberty Bell--it's good enough for me!

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)

Thanks Rod.