Another test....
With a DMM, measure the continuity/resistance between either/both AC pins and either/both connections on the output jack.
You probably will not see anything, or a VERY high resistance on the order of 1meg plus.
Yes, it is a way to reduced EMI and the coupling through the safety cap is enough to give you a tingle and should disappear when a load is connected, but if you are using a laptop that is also floating you could get a little tingle.
I don't like this because this leakage current is passed to anything you connect to the laptop like a usb device that may be earthed! Really piss poor way to reduce emi.
If you get a tingle, try reversing the AC plug if it isn't polarized, and see if the tingle goes away.
If it does, then either the supply's EMI cap is wired to the wrong side of the line, you are on a 220v circuit where both lines are hot to earth, or your AC plug in the wall is wired wrong.
Going back years with old tv sets, sometimes one side of the line was connected DIRECTLY to the chassis and there wasn't a power supply transformer.
The line was rectified, filtered and divided for the different voltages, and when you took the back off the service the set, you got a BIG REAL shock if the plug was in wrong... not to mention any test equipment that you connected the ground lead to the chassis was nailed! I know as I found out on a RCA XL100 solid state CRT tv! YEEEOU!