In that case go with an 18v transformer not 25v... 18v *1.4 -1.1 = 24.1v nominal, 26v off load. Ideally you want a 22v transformer but the only way to get one is to roll your own.

Actually there is a solution to this - its called buck windings. Basically you wind 10turns of heavy gauge wire onto the transformer and measure the voltage you get, then adjust the number of turns till you get 3v and connect that in series with the other windings in a way that reduces the output voltage from 25 to 22v. This allows you to fine tune the output voltage for a little more effort and messing about but relatively little cost (a reel of shellac insulated 14 gauge copper wire basically)