I am building a three rail layout and a g scale layout and want to us the same dcc stuff for both layouts and need to know if any one makes a dcc decoder for ac current systems.
You should look into MTH DCS.
Their system works with the HO, O, and G scale products.
There are DCC components available for three rail. Because of the power draw they aren’t cheap and because of the way the signal is encoded, you may need to do some rewiring (particulaly for older open frame motors). Digitrax and NCE make high current decoders that can be adapted for use in three rail trains.