How would you propose to "compensate" for an arbitrarily large output capacitor?  If the TOPSwitch output does not reach regulation due to caoacitive loading before the input 47uF capacitor voltage falls below its lower voltage limit, the TOPSwitch will trigger another auto-restart cycle. One possible solution to this situation would be to use a "soft finish network", which essentially closes the feedback loop around dv/dt, so feedback is provided to the TOPSwitch control pin (and recharging the 47uF control pin capacitor) even though the output is still rising and out of regulation. However, an arbitrarily large output capacitor will require a correspondingly large capacitor in the "soft finish " network.

The 500 Hz resonance limit may have been imposed to reduce the difficulty of stabilizing the loop due to the double pole introduced by the effective inductance and the output capacitance. However, the ESR zero  of the output capacitor needs to also be considered - the ESR zero is actually your friend in this situation. Polymer capacitors may be more problematic, as they can have a lower ESR compared to their capacitance, pushing out the ESR zero frequency.

Thanks, yes , i appreciate the auto-restart situation.

Thats a better point....as you know, i think it would have been better for the engineer (not yourself i apprecite) to simply remind that there is a resonance frequency of LE and Cout, and that the xover should be  suitably away from this......having the resonance ">500Hz" doesnt necessarily achieve this.....i thought there was some new info on Voltage mode controle here...but it appears not.

I have recently been trying to prove stability of a TOPswitch-HX  potential design which uses a transformer with NP/NS not supported in PI XLS or PI expert, and its not been possible unfortunately....if we could have proved stability we would have used it.....but we were not able to do so..........and now, in another post, a PI Apps engineer is saying that topswitch internals relating to modulator transfer function are PI's  IP....so basically we've no chance of making out the error amplifier and modulator  transfer function....we cannot afford a gain-phase analyser..........and the converter goes into CCM at low mains....so there is no way we will use a voltage mode converter in CCM, when there is no modulator transfer function available for it....since we cannot prove stability.

If you don't have a gain-phase analyzer, you can use the pulsed load response to check stability. You won't get any numbers for gain and phase, but you can check for marginal stability.  BTW, there is nothing wrong with a voltage mode converter running in CCM - this was done with TOPSwitch all the time in the early days of TOPSwitch 1 due to the limitations imposed by the internal mosfet RDSon.  Everyone used big mosfets with 3842 controller or equivalent running in DCM because they were scared of the RHP zero - turns out not to be an issue for a reasonable design (read not overly continuous) at 66 or 132 kHz. BTW, an HP4194A is what we used for gain-phase analysis in the early days at PI. They are big and clumsy, but they also cost less than a good oscilloscope these days on the used market That analyzer dates from the days when HP still meant quality gear. I have one at home for my own investigations.