I'm trying to design my own power supply and I decided to use flyback topology. But before chosing a controller for the circuit this question came up: how far can i get with the output power? since I will design the feedback winding for the current measurement why can't I just "fool" the controller by changing this parameter(feedback turns)?
There is no inherent limit to the power you can get from a flyback topology. It just happens to be more cost-effective for relatively low power applications. Many flyback converters control the peak current by a low-value external sense resistor in the switch source (or emitter) circuit.
I suggest auditing the Coursera courses on switchmode design (from the University of Colorado, I think). They're free to view (but unfortunately not the quizzes).
I would say the you can calculate power capability by considering the peak current limit on the primary, and the duty cycle. For boundary mode, the duty cycle is known with the constraint the magnetizing inductance must have volt-second balance. I get D = VoutNps/(Vin+VoutNps), not considering the diode forward drop. Then the input current is .5*D*Ipk, on average. Multiply that by Vin and some efficiency derating, that's the answer I think.