this is how it all works
a transformer is 2 coils of wire seperated by a core
a 10:1 step down transformer would convert 120v AC to 12v DC via transformer and regulation
now, coil ONE on this trasformer (called the primary) should have 10x more turns than the secondary
the primary is what is connected into the wall, and this coil of wire now has 120v running through it (AC of course as transformers also DO NOT WORK WITH DC)
let me say that too right now
ONCE AC IS TRANSFORMED INTO DC IT WILL NOT WORK IN A TRANSFORMER
transforming requires RELATIVE MOTION in order for the electrons in the secondary
this relative motion is achieved in AC through the 60 Hertz up and down value of +120, -120 +120 -120
in DC, there is no motion, so if you try to connect even 1 million volts DC into a transformer, you will not get voltage out of the secondary
3 things depend on the voltage created
1. Strength of magnet (the current running into the primary wire creates a magnetic field, the stronger the current the stronger the magnet)
2. # of turns on the primary and secondary
3. SPEED OF RELATIVE MOTION - this is the part that kills you, since DC has no relative motion you just can transform it back up to 120v AC once its down to 12v DC