Thanks, the same designer has also used a primary clamp snubber on the 100W flyback which comprises just a SMA UF diode going into a 220V , SMB size TVS.
(ie not an RCD clamp, or an RCDZ clamp, so no power resistor to dissipate the energy from the leakage inductance)
If i had access to the PSU then i'd thermal test this, because such a small primary clamp/snubber is unheard of for a flyback of 100W. The TVS is also on minimal land pads
the spec for the flyback is vin=418v, vout=40v, iout=2.5A.
Switching frequency is 75KHz.
Transformer primary is 560uH, and NP/NS = 3.19
Ipk primary = 2.2A
The opamp spoken of is regulating the output current of this flyback