90VAC - 600VAC input power supply - 17W

what do you mean "  we should do up to 580. After that the efficiency is not good."

please explain.

  Hi, 

  Actually it was written in the docs about stackfet... The power supply shouldn't used for > 580VAC... In your opinion, can we make a power supply whose input if from 90VAC - 600VAC with stackfet?

It is possible to make one stacked FET power supply.  As you mention, effciency is not going to be great.  Depends how much effciency you want.  If you can allow low effciency, then should not be any problem. 

  Thanks!

  Can I use the very same schematic from DI-124 (http://powerint.sphere.kharkov.com/PDFFiles/di124.pdf)? 

  Of course, I'll need to change the transformer and some components, but can I use this schematic?

You can use the same platform,  same architecture.  But the stress on each component needs to be checked 

I am also interested in a 600Vac power supply.  It was suggested to use the same architecture but check the stress on each component.  To save time and effort, does PI have any  tested power supply design that operates from 600Vac? 

You have to follow the same architecture. YOu calcultae your transformer for proper flux density at maximum voltage. You have to check the voltage rated for each component See the below link http://www.powerint.com/sites/default/files/PDFFiles/di124.pdf 

I have built the circuit in DI-124 and it works well.  However, I want to increase the maximum input voltage to 660Vac.  By changing components, can I expect this design to work at 660Vac (ie 933Vdc)?  Or is there some limiting factor that I am not aware of?

I do not have a straight yes /no answer

The only way to find out the answer is to review the complete design. With larger Vin (933VDC)  you need to review the flux density in the transformer,  the reverse voltage on each rectifier.  The stress voltage for the power switching Mosfet. 

In other words, the whole design needs to be reviewed.