What follows is pure speculation! Just a theory on what is going on with Occam's razor.
TLDR: Debris can act like 12V-2x6 was never invented.
What makes me wondering are the reports that reseating the cable connections can improve on (re-)balancing the amps on all lines. Some guy posted this recently on Reddit. I know, never trust reddit posts, but still...
This made me thinking.
Simple logic: If reseating and reconnecting the cable can improve the connection, it should also be able to decrease the quality of the connection either. That said, one can probably rule out improper connections because I think most Blackwell users (currently a small group of enthusiasts and creators own those cards at the moment) are probably aware of the old 12vhpwr connection probs. I'm sure most of them will double check the connectors, despite being 12V-2x6 cables or not, ensuring proper connections to GPU, Nvidia adapter and the PSU. I know, I would (and did check like a paranoid monkey multiple times with my 4090, e.g. when moving the rig - because I don't trust the 12vhpwr standard at all).
So let's rule out improper connections, will we?
Too make things simple let's also rule out cable quality differences (again, before you object, Occam's razor).
Let's further take into account that lab testing at Nvidia most probaly did not reveal a problem. Also, that most users (well, we don't know yet, I just try to get a statistical best guess by appearance of posts and known numbers like the microcenter lists) don't have a problem and lines are usually amp-balanced.
Also, that Nvidia stays silent at the moment. Speculation why: 1. The issue is not instantly deniable ('user error').
2. They need more time to understand the issue.
3. They need more time to understand the number of melting event and statistics (that's what you get for paperlaunching - to little statistical information).
Then only ONE probable thing is left in the equation (based on some people having a problem and most others having none) and that is what the experts call foreign debris. What if microscopic clumps of dust or tiniest lints in the cable or connector are weakening the connections to the pins from within? Then reseating and reconnections sometimes helps and sometimes worsens the connection. Obviously, the debris issue is always a problem with any cable and GPU of any Gen, but could get uglier with 12VHPWR driven at the limit. The less headroom you have, the more massive the problem. BuildZoid and some Intel engineer recently spoke about the general fragility of the 12VHPWR standard. Nvidia skipping the shunt resistors on 4090/5090 certainly did not help. And then comes the debris at 600w.
Just a theory. But testable. Someone bold (and wealthy, because you can brick things) could test this by putting a tiny speck of dust into a 12v line on a connector on the GPU or Cable or on the PSU before connecting everything. Then fire up Furmark and measure how Amps (and temps) are going up or not. Most likely, debris will produce an amps problem on a pin somewhere and thus the resulting heat will end up melting something somewhere. Because PSUs, despite having loads of safety triggers usually have no load line balance or load intelligence (exactly like the 5090 on the other end of the string) they will try to push harder and harder with debris - they will eventually shut off but maybe too late. It's all still a dumb design that gets dumber if the asking end (the GPU) is also load line dumb. Debris will then result in undetected resistance, then comes the heat, over time comes the melting, if you are unlucky and your PSU does not shut off. If this theory is true, then the effect goes likes this:
1. The more the right amount of debris(not too little, to make any difference) is somewhere in the line the more risky is the connection at full power to become imbalanced. But there are scenarios thinkable, where debris will not result in a perceivable problem.
2. Reconnecting is not a problem (even if you only have an finite amount of reconnects on any standard and a tiny amount on the 12VHPWR variants especially). But the more you reconnect the cable to the connectors, the more likely you will introduce debris into the chain.
3. Debris can act like 12V-2X6 was never invented, because it can fully block the contact at pin level, thus the system is behaving like an improperly seated 12VHPWR connector, even when you have 12V-2X6-only hardware and 100% correct connections.
4. The stronger the PSU (1500w or more should be best for trying out), the more imbalance will be there and the faster is heat generated. The 5090 asking for large PSUs does not help either. After a Furmark-while enough heat will be accumulated to start the melting somewhere in the power path between PSU, cable connection points and GPU connector.
You don't need a infrared thermometer or current clamps to do this test - you can simply test with the finger method - the cable (one or a couple of lines in it) should feel hot (if it feels just hot, it's too hot in reality, because it's probably sleeved etc., the copper itself should be way too hot then, hence resistance somewhere).
Speculation! I may be completely wrong.
