I turned a cheap CV PSU to a CC LED driver

[ElectronSurf]

It's a 1$ chinese 12V-2A PSU with a common design using CSC7203, the one I got instead of TL431 in the feedback loop using just a zener diode to regulate output voltage.

My plan was to inject a circuitry to the feedback loop to bypass the zener and by doing so I can regulate output voltage/current. The picture from Falstad simulator is showing the concept.

Note that I'm using BC556 transistor to bypass the zener and not shown in the schematic. it's soldered directly on the zener. The box was just big enough to fit the PCB and potentiometer.