Hardware

Tldr on the problem is that small differences in resistance between conductors and contacts in the cables can result in different currents in each wire. Previous cards would split pairs of pins up and have each of them current balanced (same current drawn in through each). The 40/50 series shorted all of the pins together, which doesnt allow for any current balancing on the GPU side.

Additionally, previous cards would refuse to turn on if any of those shorted pairs were not present - something the new cards can hardly detect. This could allow all but one high side wire to be cut and the GPU might not realize and try to draw all 50+A through a single conductor which is rated for <10A

The 9070xt that Steve at gamersnexus looked at which had the 12vhpwr connector also had this flawed design, but the power on the 9070xt is much much lower, so you are less likely to see a problem on those cards.