When the information about the melting and overheating issues with the 12VHPWR power adapters supplied with Nvidia's GeForce RTX 4090 graphics cards emerged, the company remained surprisingly silent and only said that it had begun conducting an investigation. In the last few days, the company became more open about the issue and revealed that it sources the adapters from two makers.
Gabriele Gorla, Director of Engineering at Nvidia, told Igor's Lab that Nvidia buys its 4-to-1 12VHPWR (four eight pins to one 12-pin) power adapters from two companies: Astron and NTK. While both adapters are designed up to the specifications defined by the PCI-SIG standards body, they are still quite a bit different 'inside' as they use slightly different contacts. Astron apparently uses double-slot spring contacts, whereas NTK sticks to a long single-slot spring contact that has lower resistance and it is easier to detach.
According to Igor's Lab, Zotac and Gigabyte have said the adapter from NTK is less prone to failure even after multiple mating cycles. Astron argues, according to Nvidia, that its adapter performs in accordance with specifications (i.e., its resistance is below 1.5 mOhm). Meanwhile, as Igor's Lab points out, Astron's 12VHPWR adapter has its thick 14AWG wires rigidly soldered to 2mm^2 soldered pads, which is a point of failure, especially for contacts on the edges of the adapter.
While Igor's Lab details how to distinguish between adapters from Astron and NTK, it is impossible to tell which of them will ship in a particular box with a GeForce RTX 4090 inside. Meanwhile, the report says that Nvidia will keep using 3-to-1 12VHPWR adapters from Astron and NTK supplied with GeForce RTX 4080, but will only use 2-to-1 12VHPWR adapters from NTK with GeForce RTX 4070 Ti boards.
To sum up, there could be multiple possible reasons why the 12VHPWR adapters from Nvidia can melt and overheat. According to Igor's Lab's sources, Nvidia-branded adapters made by NTK are considerably less prone to failure. However, no company has gone on the record with this information, so take it with a shovelful of salt.
My guess is that the RMA rate on these cards is quite low.
Actions speaks louder than words, and "Astron" just lost a major contract to their rival "NTK".
I don't think the adapter card plugs are causing the problems.
I'm thinking that if you plug an 8-pin cable into a PSU and plug the other end back into the PSU the PSU should automatically shut down - but, there are PSUs that do not have sufficient automatic shutdown circuitry that detect such things.
I don't think you can sufficiently analyze the issue without having the PSUs that were involved with the problem.
I'd like to hear Aris Mpitziopoulos' take on this issue from the perspective of his extensive knowledge of PSUs.