Fit and functioned perfectly in my AHW President water softener. My WS is over 10 years old, and I think the original transformer malfunctioned and took out the Rev-2 board. This is a Rev-9b board, and I replaced the 12Vac transformer with one from this site. Everything is working perfectly, and we will see how long they last. Shipping was very fast and earlier that originally estimated. Measured voltages of transformers,old original (12Vac, 500Ma) 17.5Vac at the board (no load) new (12Vac, 40VA) 14.5 Vac no load. PWS-1220 12VAC 20VA Class II Power Supply AC Adapter UL 12V Transformer Plug with terminals.