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I recently bought a box full of old MeanWell 9V switch-mode power supplies, to use as PSUs in microcontroller projects. When I took one apart and drew the circuit, I couldn't understand how it was working, until I realised that the TL431's Reference and Cathode pins were swapped. It uses the TL432 format, and yet the chip has TL431 written on it. Hours of fun (if you like that sort of thing).

 

 

See also

Reverse-engineering the TL431: The most common chip you've never heard of...
https://www.righto.com/2014/05/reverse-engineering-tl431-most-common.html

 

Here's the circuit of the low voltage side of the MeanWell GE12I09-P1J power supply:

 

 

Here's a manufacturer's presentation, useful if you are designing your own circuits using this [ancient but cheap] chip.
But these days, for high power devices (>75W), you need to implement power factor correction PFC (EU standard EN61000-3-2), so use a modern chip which does that too.
https://www.onsemi.com/pub/Collateral/TND381-D.PDF