truenoteno said:
enough power to run a 24 port hub.
probably need around 14 volts at 4 amps max
(just an educated guess)
Your requirements get worse!. Now you're wanting a 56 watt mains power supply that takes next to no room - a 56W PSU by definition is going to be reasonably large.
1 other thing, could i use a tiny transformer to use as the input voltage (rectified first) for a PWM ? < 40v, then use the PWM to step down the 300VDC ?
I don't really understand what you are asking, it doesn't make much sense!. I've got a SMPS transformer in my hand this very second, it's out of a satellite receiver and probably rated at about 50W or so - it's roughly 35x35x35mm. I'm presuming that's too large for your requirements?, plus you need all the rest of the control circuitry as well.
Perhaps you should start right from the beginning, and try telling us what you are wanting to do, why it has to be so small, and why this possible hub doesn't already have a PSU?.