Electrical – “Creating” a ground pin for the laptop

Is there any danger in bonding the DC- output to Ground with a short wire, to ensure my circuit ground is also referencing the home ground? I'm not sure simply letting the outputs float is wise,

Assuming the power supply is properly built either is fine.

Side-note: I have an after-market laptop supply that's two-prong... it works either way, but if I plug it in one way the metal trim on the laptop has an interesting "buzz" to the touch. Not shocking, but definitely noticeable. I suspect that when it's plugged in the right way the output ground is weakly referencing neutral, and the "buzzy" way has the output ground weakly referencing line voltage (it's floating - it'd be quite a bit more than buzzy otherwise). The OEM supply with the 3-prong plug? Fully grounded to the shield of the DC power cord.

Power supplies without an earth connection often have problems like this, especially as they get larger.

Capacitors have to be placed between input and output to control EMI. In an unearthed design this ends up with the output being "weakly referenced" to the input. How weak that reference is (or to put it another way how big the "touch current" is) depends on the size of the capacitors. Unfortunately there is a tricky compromise here, bigger caps are better at suppressing EMI but produce larger "touch currents". Larger power supplies tend to suffer worse from this than smaller ones (this is why laptop PSUs from reputable brands are usually earthed while phone chargers are usually not).

In an earthed design this can be mitigated either by tying the output to ground (pretty much universal in in desktop PC power supplies, occasionally seen in laptop supplies) or by splitting the EMI suppression capacitors into two parts, one from output to earth and one from input to earth.

From my knowledge:

Floating power supplies can be measured with a multimeter in AC mode in regards to ground, in my case, axp power wall plugin. It will measure 130 Vac, it will give out 12 V dc, but remember this is not entirely true. Instead, you will see a sinusoidal signal on both the + and - output. This is perfectly fine, as you put the minus on the PCB ground and the plus on your Vcc, so the voltage in between those two will always measure 12V dc. Now what happens if an external grounded device, like usually USB comes into play.

You will connect a real 0V GND to the 130Vac gnd of your PCB, now if you hit the zero crossing, of course nothing is going to happen. If you hit the 130V point, you will actually shorten 130V to gnd, since there is not a lot of power behind those 130V. Most of the time it simply turn to 0V without nothing, but sometimes, USB will be reconnected or µCs will restart or or or...

So I am also curious on how other engineers found a solution to this problem, as I am constantly struggling with this.