Here we (maybe) go again: Reports from a handful of early adopters of Nvidia's new GeForce RTX 5090 graphics card are reporting that their power cables are melting (so far, there's at least one report on YouTube and one on Reddit, as reported by The Verge). This recalls a similar situation from early in the RTX 4090's life cycle, when power connectors were melting and even catching fire, damaging the GPUs and power supplies.
After much investigation and many guesses from Nvidia and other testers, the 4090's power connector issues ended up being blamed on what was essentially user error; the 12VHPWR connectors were not being inserted all the way into the socket on the GPU or were being bent in a way that created stress on the connection, which caused the connectors to run hot and eventually burst into flames.
The PCI-SIG, the standards body responsible for the design of the new connector, claimed that the design of the 12VHPWR connector itself was sound and that any problems with it should be attributed to the manufacturers implementing the standard. Partly in response to the 4090 issues, the 12VHPWR connector was replaced by an updated standard called 12V-2x6, which uses the same cables and is pin-compatible with 12VHPWR, but which tweaked the connector to ensure that power is only actually delivered if the connectors are firmly seated. The RTX 50-series cards use the 12V-2x6 connector.