I have a transformer that I took from a broken digital clock/radio it plugged directly into the wall. It looks like it says its output is 12v. It is pretty small no larger than 1 inch by one inch. If I plug this into the wall will it suck tonnes of current? Should I put resistors to limit the current. Sorry for being vague. If more info is needed Ill try to get it.

 

More info is needed. What is the load on your transformer? How many amps in a "tonne?"

 

I want to use the transformer as part of a cap charger and by ton i mean a lot as in many many amps

 

"Many" is a realative term. I could say "Yes, absolutley" or "No, never ever" and be equally right. I will therefore say "maybee, depending."

Do you have a schematic for your cap charger? A website where you got the idea? Anything at all that can provide some indication of the load?

Without knowing the load, we cannot use Ohms Law to predict how much current will be drawn.

 

Since the size of the transformer you have specified is 1 inch by 1 inch this type of transformer donot have a current rating of more that 500mA. ie at maximum you can get 500mA at the output without burning it.
So the power rating of this transformer comes out to be 6Watts , make sure you are not drawing a peak power of more that 6 Watts in your application.