Hi Eugen,
Do you have exisiting harward design using ADP16xx? What is the efficiency at full load?
What are your requirements on the control loop response? ADP1047 can be used as DC-DC design. Since the ADP1047 is originally designed for PFC, it cannot provide fast control loop response. If you need fast control loop response, the ADP1055 is best fit. This part is voltage mode DC-DC controller with fast control loop and additional pole/zero. The additional pole/zero is helpful for stabilizing the control loop for Boost, Sepic, Buck-boost type converters.
Since the output power can be as high as 400 W (500 V *0.8 A), the pseudo isolated converters like current fed push pull can be a good option for providing higher efficiency.
If you do not mind, please provide a diagram/schemaitc by mail so that I can get back to you with more suggestions on hardware changes.
BR/
James