On Fri, 10 Mar 2017 10:55:09 -0000 (UTC), Diesel
wrote:

Fri, 10 Mar 2017 07:55:44 GMT in alt.home.repair, wrote:

On Fri, 10 Mar 2017 01:58:15 -0000 (UTC), Diesel
wrote:

I prefer the ones that dont, because, sometimes, the
3 prong ones generate unwanted background hum when fed to external
audio amplifiers while plugged into their chargers.

That implies that the ground is connected to the DC common. Not sure
why they would want to do that unless it is just for RF filtering.



I've suspected the issue is a ground loop based on prior experience
with that...I haven't tried to open one of these and take a look
inside, so it's entirely possible it is connected, but, due to some
filtering circuitry in between, I'm unable to do a simple continuity
test on it. By unable, I mean that it doesn't read as completing a
circuit when tested in that manner.


http://www.channld.com/hum.html

This works well to remedy the problem...

https://www.amazon.com/Mpow-Ground-I...F6E7CCRCVEDNNN


Reading with a meter you will be looking through the filter so YMMV on
what kind of continuity you see but at 60hz there will be some pass
through. I have had that problem with desk tops that feed amps,
particularly if there are other things in that loop like a TV.