I dont have a very in depth experience with power electronics, but for all I know about SMPS, it uses a feedback network to regulate the output voltage. So what I was thinking is, if I replace feedback resistor network with a potentiometer, I can vary the feedback value, and since SMPS always tries to adjust it to the Vref, I might be able to generate the desired output.
But I strongly doubt if this will work, since this feedback is before the transformer I guess and these high frequency transformers are very much specific to their input voltage.
Let me know if I'm missing something or I'm wrong somewhere.