[sdiy] +/- 15v from a wall wart...

[Oakley Sound]

 > Depending on the capacity of the wallwart and the load you can 
usually get away with 9VAC for +/-12VDC, 12VAC for +/-15VDC, etc.

Although this is true to some extent, I wouldn't rely on it. One of the 
reasons we can get away with it more in the UK is that our voltage is 
still mostly 240V and not the 230V these wallwarts are specified to work 
  with. I also suspect that these wallwarts also have the same 
transformers as their continental European versions which can probably 
still work on 220V.

I am also thinking that the quality of mains transformers has gone down 
of late. The specs are good on paper, but more often than not, the 
transformers are producing higher voltages than they should and they 
certainly hum more. Core losses are higher perhaps due to slack 
laminations? The prices have come down though - which probably means 
that they are now made in China with perhaps less care to QA than they 
would have been when made here.

Tony