[XCSSA] Can you break transformers?

[X-otic Computer Systems of San Antonio]

I'm not sure how I'm doing it but it appears as though I've killed  
both my C64 PSU and now another 12VAC wall-wart. The thing is, I was  
able to get inside the wall-wart, and all I found was a transformer.  
No fuse or anything. However, before I started tinkering with things,  
my multimeter showed about 15VAC from the thing (I guess 12VAC assumes  
it's going into some sort of rectification/regulation? Well, my  
initial tests with my new power board worked great - I was getting the  
DC voltages I was expecting (namely 12 and 9VDC). Well, I hooked up my  
PIC board without the PIC itself and got the proper voltages. Then I  
stuff it with chips and, after that, now my wall-wart reads 3VAC with  
no load.

It's just spools of wire! How in the heck am I so good at nuking these  
things? :P Any thoughts?

Good news is that I have other adapters, but they are DC and while  
it's not a big deal it's likely going to be fantastically noisy for my  
SIDs :/

Help would be appreciated!

Tim

P.S. Frederick, if I can figure out how to keep my MidiBox SID powered  
up, I'll go ahead and test your SIDs next :)