> I think you're catching on.  What makes this discussion kind of
> confusing is there are generally two kinds of plug-in adapters:

And what is even more confusing is that battery chargers are not
power supplies, they are what they are - battery chargers. This
means that using them for anything else other than what they are
designed for will lead to strange things happening. They usually
do not have a smoothing capacitor, why? because the batteries
are the capacitor, think about it, a 1.2v nicad battery will 
immediately soak up all the ripple, so you don't need a
capacitor. On the other hand, connect to a pic, and expect 
a burning smell to tickle your nose.

> 
> 1)  Old-fashioned "wall-wart".  AC input->Transformer->diode
> bridge->big capacitor.  These are not very well regulated.  Due to
> resistance in the transformer, the output voltage goes down as you
> draw more current. At no load they generate a voltage about 40% above
> rated. At the rated current, should output the rated voltage.  If it
> is made for charging only, the capacitor may be omitted or skimpy. 
> You can compensate with a bigger capacitor in your circuit.
> 
> 2) New-fangled "brick".  AC input->rectifier->high-DC
> voltage->switchmode regulator->output.  These are useally pretty well
> regulated to the rated voltage and ripple should be pretty small too.
> 
> It sounds like you've got the second type.
> 
> If you don't have a scope, you can measure ripple by setting your
> voltmeter on AC volts with a capacitor in series to block DC. (most
> multimeters have the capacitor built-in for their AC range, but some
> analog ones don't)   Ripple will go up as the load increases, so
> measure under the load of your circuit.    Note, the ripple is not
> exactly sinusoidal, so RMS readings will be slightly inaccurate with
> this method and a typical cheap meter.  Still, it's in the ballpark to
> tell you if ripple will be a problem with your supply or not.
> 
> Regards,
> Mark
> markrages@gmail
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