On Tue, 11 Dec 2012 19:15:00 -0800, Robert Baer
wrote:

* I have opened many unregulated wall warts,from el-cheapo to
top-of-the-line, and NEVER seen any thermal fuse, period.

Well, they're normally hidden under a layer of insulating tape on the
transformer (in series with the primary), so a casual examination
might not detect it.

If they're UL class 2 they need to limit- in some cases they've made
the winding self-fusing, in others they use a thermal fuse. I don't
think self-fusing* cuts the mustard world-wide with the safety
authorities, so I've seen mostly thermal fuses in approved linear
adapters these days.

Eg. http://www.cui.com/Product/Resource/...0050-P5-SZ.pdf
... has a 130°C thermal fuse

I can't share the spec sheets of the ones I source, but they specify
the thermal fuse rating and UL/CSA approved part numbers and
manufacturers.

Crappy design as they all put out more voltage AT FULL LOAD thantheir
"specification".

Not what I've seen. They put out the spec voltage at full load.
* I have NEVER seen an unregulated wall wart like that,ever.
And i have seen an un-countable number of them in (about) 40 years.

What are the test conditions? The ones I've bought in production
quantities do what the specs say, the test reports say, and what the
label says, under the appropriate test conditions. If they didn't meet
the specifications at incoming inspection they'd be sent back! Did you
adjust the input AC voltage to the specified voltage and put an
accurate programmable load on the output? They always read a LOT
higher with a light load, some are 50% worse than others.

Now, even the el-cheapo regulated ones (eg: linear series pass) do
meet label specs.

Where do you find those? I was looking for some and they don't seem to
be very popular these days. Twenty years ago, they were more common.
It's kind of stupid to put the regulator in that little box- easier to
get rid of the heat elsewhere and not have to worry about the voltage
drop in the cord and connector.

Switchers are better yet.

For some things.. some of the cheap crap ones are missing Y caps so
they have (unspecified) HF common mode noise on the output relative to
earth. Some of the ones that have Y caps are using unapproved and
probably unsafe caps. Many of them have a lot of ripple and are
pushing the output caps hard enough they'll likely die sooner than the
linear unregulated adapters. Cheap ones may be missing common mode
input filters so they'll conduct noise.

* with self fusing, the wire insulation melts, causing shorted turns,
which draws enough current to fuse the copper wire or to blow a
non-thermal fuse in series with the primary. Since copper melts at a
higher temperature than the tape and fish paper can withstand, it has
to be shown that it won't compromise isolation.