> IMHO, the best overvoltage protection is a label:  12V 250 mA.  If
> the user violates that label, it becomes his or her problem, not yours

I'd agree with you generally, if I'm in a libertarian mood - except to say
that sometimes (well, a lot of the time actually) people need protecting
from themselves

I've had the case of someone who stuck 12V up a prototype instead
of 6V in the vain optimistic hope it would "go faster". For a few ms it
probably did, then and forever after it go-ed no more. As he was the
only user and the PIC and LCD were obviously frizzed and he ignored
my instructions, he had no option but to 'fess up and pay for repairs. I
could have protected the circuit but I never expected such a reckless
experiment

But on the flip-side there's the example of whoever the someone was
who moved the voltage selector on my nephew's PC from 230 to 110.
No smoking gun (although the PC made a passable stand-in) and no
obvious culprit - "I didn't do it" "It was like that when I got here".
Awkward

A label is a good cheap idea but you have to consider what the user
does with the unit after its trashed, and how that may impact on your
reputation and conscience

As for the OP - if you don't want the protection on the PCB how about
making a small protection board that can be used during prototyping.
Include a rectifier (diode bridge + cap), regulator, LED and filtering.
Then you can use whatever PS is available and know that only a safe
stable 5V will get to the main circuit

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