[sdiy] power supply reverse polarity protection

[Dan Gendreau]

> A thing that is more threatening is wrong polarity.
> It may happen during construction , on the work bench
> or with self made lab equipment (banana plugs)
> that power supplies are swapped to the wrong.

I seem to remember building a kit a long time ago that had a bridge rectifier in
the power supply for this reason. It allowed you to use an AC or any polarity DC
power supply.

-Dan G.