Working from this datasheet for the Mosfet/controller combo:
http://www.farnell.com/datasheets/26251.pdfYour unit should have a mechanical mains switch so any configuration parameters for the controller are likely only to be soft start. Read the bit about fault conditions in Shutdown/Auto-Restart on P9.
Looking at the typical usage circuits from P20 on we see the divider and dropper from HV DC are 1/2 W which suggests they are under a little stress and if they drift wildly it'll upset the input into pin X. The dropper into pin L need be checked too.
Further to those mentioned the series diode between the secondary and the opto need be checked along with the main polarised cap, in all examples shown as 47uF that indicates it's for bulk storage for the C pin.
Another possibility is the other smoothing polarised cap before the opto or the ceramic between C and ground(if fitted).
Failing all those you'd look hard at the secondary side LV diodes and caps IF there is not a short on the mainboard that's pulling the rails down and putting the PSU into External current limit mode.
One of the rails from the PSU is only mains Line reference for the Trigger....work out which one it is and exclude it from investigations....it won't be affecting the PSU startup.
Spend some time reading this datasheet to understand it fully and work your way through sections of the PSU circuit, eliminating them as suspect as you go.
Tip. The feedback circuit will be on probably only one of the rails....concentrate on that rail initially.
Oh, and the PSU section in the linked Siglent service manual is on P46.
Good luck.
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