If you have an older Clack Control Board that requires AC ( will not work with newer DC transformer ),
you can use any 12 volt AC transformer of 500 ma or higher as the power source.
Just cut the wire off your old transformer ( close to the actual transformer ),
and connect the two wires ( one white and one black ) to your AC transformer.
NOTE: Since it's AC ( alternating current ) there is NO Polarity, so it will not matter which wire is connect to which connect to your replacement transformer.
And just so you "know", it's only the Black Wire and the Outer White Wire that are used.
The two "Center" White Wires are NOT used ( that are just there to hold the "space" in the 4 pin connector used with Clack power connections to their boards.