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.