On Sun, 14 Dec 2008 03:42:08 -0500, mm
wrote:

On Sat, 13 Dec 2008 23:42:49 -0700, Tony Hwang
wrote:

mm wrote:
I was looking at an FAQ for some small appliance that runs or
recharges from an AC adapter, a black box that plugs into the AC and
lowers the voltage to 12 or less, and maybe changes it to DC.

And it said this was safe, and I too have been assuming these were
safe, but...

I have never heard of ons shorting from the primary to the secondary.
Usually they burn out the primary - occaisionally the secondary on the
transformer type - while the switchers also fail "open".