Re: "my backpack can weigh between 8 and 14kg"
The AC ground was originally placed there to make it less likely that you die due to equipment failure.
Consider what happens if the isolation fails and the case or output USB shell becomes live.
If there is an AC ground connection to the case etc, a lot of current flows and the fuse blows, or circuit breaker, RCD or GFCI trips immediately. You notice that the device has a fault and repair/replace it.
If there is no AC ground, then it is likely no current flows. The device even continues to operate. You do not realize there is a problem until you have received an electric shock. The shock won't be large enough to blow a fuse or trip a breaker, so if there is no RCD or GFCI, the shock may continue until you are seriously injured or die.
This is how AC ground protects you from death and injury.
BTW - The main difference between the US and the UK/EU is that the US electric codes primarily care about fire. Individuals can fry, they don't care unless the building burns down as well.
Biting the hand that feeds IT
