Not much. Minor improvements in efficiency and the 12VHPWR connector is improved with a new 12V-2x6 connector so that the GPU shuts off if the connection comes loose. There was this power connector melting issue with the RTX 4090 which is the reason behind this. I don't think you should face a issue with the 70 series GPU as long as the cable is plugged in correctly (that's why MSI has changed the color to yellow of this specific connector). But better to ask other members here first.What are the advantages of ATX 3.1 over 3.0.
The connecting cable is the same. You can only tell the difference by the label on the connector. H++ is 12V-2x6 (ATX 3.1) and H+ is 12VHPWR (ATX 3.0).
Would love if anyone with more details about this ATX 3.1 vs ATX 3.0 mess can help clear things up. Seems like a shitshow because they had to change the specifications so quick after introducing ATX 3.0 lol.