Blue secondary cable from transformer ktb-105 to light fitting?

There will be 4 connections - two for mains input from the switch / dimmer and two for output to the 12 V light.

If more than one light then the lights will be connected in parallel

The colours are of no consequence although the EU convention for mains power is Brown = Live and Blue = Neutral

And remember Lord Finchley...

Lord Finchley tried to mend the electric light
Hinself. It struck him dead and serve him right.
It is the business of the wealthy man
To give employment to the artisan.

Good Luck...
September 2016

Does the picture here help? Primary and secondary connections clearly marked

http://archiwum.allegro.pl/oferta/zasilacz-do-halogenow-kaoyi-ktb-60-20-60w-okragly-i4405355476.html

Anon
September 2016