I'm a little skeptical about the effectiveness of power supplies, particularly on the LP12. Don't get me wrong, I'm sure a better PSU will do a better job but how much of a difference it really makes is a big question mark for me.
Why? Well firstly, I don't find the evidence very compelling. I've searched the net looking for opinions and information on the various LP12 power supplies and definitive conclusions are hard to come by. Few people have compared multiple supplies and you find opposing opinions. Some might say the Herc sounds better than a Valhalla, others say it sounds the same. Importantly a new PSU usually involves a general tune-up and it's very common for people to have other upgrades fitted at the same time. Watching LP12 forums that's usually the case, the deck goes to the dealer and has a service plus a few new parts fitted including the new PSU.
That's a problem obviously as you can't separate the effect of the PSU from the other changes that happened at the same time. And even when people do feel they can describe the effect of the PSU, praise is generally not very specific and faint when it is. Meaningless audiophile terms like 'massive' and 'huge' aside, you usually hear talk of a little more 'blackness' or more detail but you're looking at a slight improvement here, no matter how you cut it. Which actually makes sense you you consider the physics.
From a speed stability perspective, the LP12 is not brilliant. The platter is nice and heavy, about four and half kilograms, but it bobs on springs while the motor driving it is bolted to the world. So the motor and platter are free to float around relative to each other, connected only by a very flexible and stretchy rubber band. By far the biggest contributor to the speed stability has to be the flywheel effect of the heavy platter. Which by design is going to iron out fluctuations from the motor and belt.
When I bought the Rega RP10 one of the very first things I noticed was that the speed stability was much better than my LP12. Which made sense as it also had a hefty platter but was a rigid deck with a sophisticated motor power supply. And two rubber bands! I couldn't get on with the deck for other reasons though so went back to an LP12, a different deck which I built up myself. But here's the thing. The new LP12 has better speed stability than the last one and I would say it's pretty close to the RP10. It's certainly very good and I don't hear the speed fluctuation being a problem like it used to be. I'm happy with it.
And the fantastic power supply that delivers this? The Magik! A PSU I thought would be a stop-gap. The old deck had a Norton and I've use the Avondale TAPS, Valhalla and Basiks as well. So why is it better? I'm speculating but I think it's the set-up. The design of the LP12 makes this important, I spent a lot of time on it and came up with a new way to dress the arm cable. Which is something I think is critical to speed stability on the LP12.
There are so many variables on the LP12, both in terms of set-up and specification, that I think it's very difficult to isolate the effects of the PSU. At any rate, I think the differences are relatively small and quite poor value when looking at the big Linn PSU options. Getting the deck set up to within an inch of its life probably gives you more of an improvement than a Lingo4 on a deck that's sub-optimal. And from the pictures I've seen, sub-optimal looks very common.