Class 2 Power Supply

Are you sure about the AC output? If so, all you need is a transformer. If you mean 12V_DC, you'll find thousands of them with Google.

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I assume (I know) that the ratings you've specified come from the existing power supply which is presumably (ditto) no longer working. And, you presumably, are asking what you can use in its place?

What you need is almost any power supply rated to deliver 12 VAC at 1800 mA. You might use any power supply that can deliver 12 VAC and at least 1800 mA. if it is a well regulated power supply. Some of those little "power bricks" have no regulation--the only "regulation" supplied by the load--thus a higher rated one might deliver a much higher voltage at no load (or below rated load) that could damage your speaker system.

You might also get away with one that delivers 12 VAC at less than 1800 ma. if you don't use it at high volume levels. (You might also get distortion in that case.)

this place has many to choose from. http://www.digikey.com/

I may be dumb, but I had a heck of a time trying to find a 12 VAC transformer there (with their paper catalog, no problem).

So, I googled on ["power supply" "12 vac" 1800ma]

Here's one that will do the job from http://www.fitnessrepairparts.com/part_search/CatalogSearch/ac%20adaptor/25/0/225

AC - AC Adaptor, 12 VAC, 2500 MA

Wall mounted AC adaptor, Input = 120 VAC, Output = 12 VAC @ 2500 MA - Unregulated

Ignore what I said earlier about regulation--I was thinking more of a DC supply than an AC supply, you won't have a problem with this.