isolated dcdc converter

Hello everyone I'm collecting ideas, plans, projects, tutorials, appliction notes etc ... to make a dcdc block which I give the specific in figure below smps.jpg



I'd like to be able to adjust the maximum current.

Could you help me advising for example pwm controller to be used (Texas, Linear, ...), the method by which to adjust the current and the configuration best suited to achieve my dcdc (forward, flyback, puspull)
For now, consider the purely resistive load.
thank you very much

How critical is the 250 volt output? Does it need to be with in 1%?
How critical is the 0.4 to 1Amp? If I measure form the secondary side it could be 1% or better but measuring from the primary side will be only 20%.