This is probably very basic, but...
You can wire the transformer AC through the buck converter, run the transformer to max AC and measure the output at the DC end of the buck converter. Adjust the DC Buck Converter output voltage down to 9.5 volts (or the maximum you would ever want). That prevents you or others from grabbing the wrong output handle on the transformer, and smoking your LEDs.
Then gradually turn down the transformer AC voltage until you reach the lighting where everything works and you get the level you like. Obviously, using a fixed output like a power brick, or wall wart, that is already at max output.
Realize that LEDs (a) like DC better than AC, (b) turn "on" at some minimum voltage, and (c) burn up at very slightly above the rated maximum voltage. In the middle there is some dimming or brightening though not like with an incandescent bulb.
The lower you run the building lighting etc. and still get your results, the easier on the accessories/ longer life. I almost always run everything at the minimum.