Massive sparks from HDMI cable

[freak]

We had a user with a Dell Vostro laptop attempt to plug in an HDMI cable from a TV to a USB port.  He didn't force it.  He simply touched the metal shield of the HDMI cable to the metal case of the laptop not realizing that it was the wrong port.  The laptop was being powered from it's original charger (3 prong) that was plugged in to a grounded power strip which was plugged in to a grounded outlet.  The TV was plugged in with it's original 2 prong cord which was plugged in to a grounded outlet.  Instantly there was a massive flash of sparks about like you would expect if you touched mains hot to neutral.  We have it on video however the HR department won't release it.  I do have a still shot.  No one was hurt, shocked or burned in any way.  The cable shield and laptop case are visibly burned.  The laptop charger no longer functions.  It does not trip a breaker or heat up up when plugged in.   Just no output.  The laptop works ok and will take a charge through USB-C.  We plugged a exact replacement working power supply into the barrel connector socket on the laptop.  Instantly the charger light on on the barrel connector goes out and the charger whines.  We unplugged it right away and it still works as tested on another laptop.  I checked the outlets involved and the hot, neutral and ground all had readings like you would expect in the US.  The laptop and non-functioning charger is being sent out for repair.  The TV appears ok and we tested it with another laptop without incident.  I know it's difficult but anyone want to speculate on a cause?

[madires]

Is anything else connected to the TV? A set-top box, cable TV or satellite TV?

[freak]

No.  Nothing else.

[Jeroen3]

One of the power supplies has lost primary insulation in the transformer or y-capacitor. Possibly the TV's, because it has no earth prong.
It could also have been some other appliance attached.

[wobbly]

Does the HDMI cable run a long way through the building?

[BrokenYugo]

I would think it has to be a power supply fault in the TV, no other path in the setup described. Was the second laptop on a 3 prong charger at the time?

Definitely looks like a 120V short in the pic, the one time I saw it happen (iron bedframe rail hopped over a plug plugged into the wall, hard L-N short for a split second) the breaker didn't trip either.

[JustMeHere]

I'd get one of those socket testers and test your wall sockets for a wiring fault.  For example, a socket that has hot and neutral swapped.