Stack Audio's Alto PSU or Vinyl Passion's revolution 2 for Linn LP12 ?

+1 for Stack too. He is more if a Linn specialist.

I've heard neither, but I like the engineering philosophy behind the Stack Audio unit better.  The Vinyl Passion unit appears to be a Lingo condensed down to a Valhalla sized unit.   However, I think the addition of Vinyl Passion's Linn motor clone with the more precise pulley and thrust bearing would be a very worthwhile upgrade.  I have mixed feelings about making synchronous motors closed-loop (ie, monitoring speed feedback).  While absolutely essential for DC motors, AC motors are dependent on frequency to achieve speed stability - a lot rests upon the controller to make these changes rapidly enough to be transparent and not result in either motor cogging or 'hunting' for speed lock.  Alas, the best AC synchronous motor controller I've heard was an open-loop design made by Mark Kelly, the Synchrotron AC-1, which allowed fine tuning of ever parameter of motor performance. Good luck finding one.

Of course, the best option is to ditch the old fruit box, and move on to a modern turntable.  Best thing I ever did. Just my 2¢