You could try to increase the frequency by adjusting R516: When the resistance gets lower, both the frequency increases and the duty cylce decreases, reducing the peak current. If it does not reduce the current, you could also try removing all secondary side diodes.
The power supply came set at 142 KHz, the maximum i could set up with R516 is 145 KHz, unfortunately.
If one of the windings is shorted partially, the peak current will be much higher. If you have a LCR meter you can try to measure the inductance, but you probably have to desolder the transformer to get correct measurements. The inductance is probably in the range of 500uH to a couple of mH. It can be higher, but it should not be lower.
Transformer was removed and tested after i checked the MOSFETS in the beginning, i only tested the transformer at 1KHz though:
4-6: 2 mH/660 Ohm
1-7: 10uH/0.2 Ohm
2-7: 1.97mH/418 Ohm
10-9 and 10-11: 40uH/0.8 Ohm
15-14 and 15-16: 9,9uH/0.2 Ohm
2-7 and 4-6 are slightly different but probably should be identical (1:1 windings), that might imply a small winding short in the beginning or end of 2-7. Still not a good explanation about the power uptake in idle when applying 20V. Will have a look at the MOSFET output and winding outputs with the scope tomorrow.
BTW, i've removed all secondary diodes before the D525 tests to make sure there is no influence from the secondary side.