I have a transformer based AC fan controller (rated for 230V input) with five output steps ( 230V(5) - 200V(4) - 160V(3) - 140V(2) - 125V(1) ). I would like to have more fine grained steps, and am thus thinking to connect two equal transformers in series, giving me a total of 25 different steps.

The second transformer would then get as input the output from the first transfomer (125V-230V). Is it likely that this would work (assuming there are no other components inside the controller which requires 240V)? In other words, does a transformer work well with any voltage below the rated voltage?