Corsair Readies New 12VHPWR PSU Cables For NVIDIA's Leading Lady Lovelace
That will not only save you the hassle of having the extra cable-length from the adapter in your case (and the ugly sight of mid-cable connectors), but also allows the new video cards to draw more power from the PSU. Corsair says the extra four sense pins are connected and configured for 600W operation on compatible power supplies, although that apparently only includes units rated for 1.2 kW or more.
Besides the new PSU cables, Corsair also has Hydro X Series waterblocks on the way for NVIDIA's 40-series GPUs, too. The company says that they're "full-conversion" waterblocks, so they completely replace the air cooling on the GPU. According to Corsair, they should allow you to "squeeze every drop of performance" out of Ada Lovelace, and they'll naturally include integrated RGB LED lighting. These will be available in November.
If you're after one of those 12VHPWR connectors, you can order the cable immediately from Corsair's web store for $20. The company says that they'll be shipping those out starting September 29th, so you'll have plenty of time to admire the wire before you get your RTX 3090 in October. Corsair has a modular PSU cable support matrix that is supposed to show which units can use the new cable, but it doesn't appear to have been updated yet. Maybe check back in a few days.