> TL;DW: The 3090 had 3 shunt resistors set up in a way which distributed the power load evenly among the 6 power-bearing conductors. That's why there were no reports of melted 3090s. The 4090/5090 modified the engineering for whatever reason, perhaps to save on manufacturing costs, and the shunt resistors no longer distribute the power load. Therefore, it's possible for 1 conductor to bear way more power than the rest, and that's how it melts.
> The only reason why the problem was considered "fixed" (not really, it wasn't) on the 4090 is that apparently in order to skew the load so much to generate enough heat to melt the connector you'd need for the plug to not be properly seated. However with 600W, as seen on der8auer video, all it takes is one single cable or two making a bit better contact than the rest to take up all the load and, as measured by him, reach 23A.
https://old.reddit.com/r/hardware/comments/1imyzgq/how_nvidi...