What you have is almost certainly an inverter for lighting although the output at 14V is a little high. The basic theory of power supplies and transformers is as follows:
1) Transformers ONLY work on AC. They take the 230V mains voltage and step it up or down depending on the ratio of turns between the primary coil connected to the mains and the secondary coil. So, if you have 200 turns on your primary and 10 turns on your secondary then the ratio is 20:1 and a 230V input will give an 11,5V output.
2) To convert AC to DC you need a device called a rectifier or diode. In theory a single rectifier can be used to do the job but most power supplies use a device called a bridge rectifier that contains four diodes in a single block. This gives you a DC voltage but there will be a lot of hum.
3) After the rectifier there is normally a capacitor, and in power supplies it's going to be a fairly large device in a metal can. This capacitor smooths out the peaks and eliminates most of the remaining hum, it also stabilizes the output voltage a little as the load varies.
4) Finally, if the voltage across the capacitor is too high you can step it down using a regulator. This circuit is normally a single chip plus a handful of components to ensure stability.
The following link shows the complete circuit:
http://www.eleinmec.com/figures/016_04.gif5) There are also units called switched mode power supplies that still use a transformer (that's what you have) but they work on different principles and they are not easy to modify as they are more complex.
Finally, a request. power supplies involve access to mains voltages and if you're not happy dealing with them or you don't know what you're doing PLEASE ASK FOR HELP. In any event it's a good idea never to work on mains powered circuits alone.