Carl; first off, breath. Maybe go out on the porch and breath some of that crisp Kentucky air.
Bill, who posted above, watches the used guitar market closely, so I think his opinion is worth considering. He stated that if the guitar you're looking at is in good shape, $2800 isn't unreasonable, even without a power supply, but I wouldn't go much higher. Now, the guitar you are looking at does have the power supply; so I'm thinking the $3,000 amount is still reasonable.
Now you've mentioned that you've been told that the power supply has some sort of short. With knowing any more about the problem than that, my guess is that a short should be easily repairable by a qualified guitar amp repair person. One reason Alembic power supplies are expensive is that Alembic only uses high quality mil-spec parts; but the power supply circuitry itself is not overly complex, and a local qualified tech should be able to sort it out quickly and easily. If the tech determines that a part needs to be replaced, they can probably get the part shipped from Alembic.
Oh, and Series instruments, when run without the power supply, go through batteries fairly quickly; so yes, the power supply is necessary.
Now what intrigues me is that this guitar has four switches. If this guitar has not been altered but is all original, then this suggests to me that perhaps this guitar has what are known as mellow filters. These appear to be fairly rare, I haven't seen many show up here on our discussion board. So, if this is indeed the case, then I would tend to think that this makes the guitar just a little more special than it already is.
