A post here clears up some of the mystery I think: https://pinside.com/pinball/forum/topic/wpc-transformer-help#post-7087874

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I contacted Homepin back when I was looking for one ( ended up sourcing one from a member) and this was their reply:

"Thanks for your enquiry.

Actually we make a lot of the Bally SS transformers and are working right now on a current order of 100 sets for one of our agents.

I have investigated the WPC transformer/s and also had several conversations with our local transformer factory about the best way to build these. There is a small issue in that there are two main types that have different audio supply voltages. It was agreed with the winding factory engineer that it would be best to make a universal transformer that has taps for both the 12 and the 18 volt audio windings to make the replacement truly universal.

Currently we are building huge quantities of mechanisms and parts for our new release pinball machine "This is Spinal Tap Pinball" so we are exceptionally busy. After TAP is actually in production I intend to progress the WPC transformers but this isn't likely to be for at least a few months yet.

Then there will be shipping to our agents so they probably won't be available in your area until the end of this year at a guess.

Hopefully you can find a used one in the meantime or can wait until these are ready.

Regards,

Mike Kalinowski

Homepin Taiwan Company Limited"