It seems some 4090 owners are unaware PSU manafacturers have 12VHPWR connectors available. Here is a list of solutions for you to avoid using the including adapter which is causing problems. PSA :
Corsair Now Offers 12VHPWR Connector Modular Cable Capable of Delivering Up to 600W
600W PCIe 5.0 12VHPWR Type-4 PSU Power Cable
Corsair 60cm PCI-e 5.0 12VHPWR 2-way 8-pin Cable for GPU RTX4090 RTX4080 Series - Black - DazMode
Corsair 12VHPWR adapter pcie 5.0 - is this normal : r/nvidia
Corsair 600 W PCIe 5.0 12VHPWR Typ-4-Netzteilkabel in Düsseldorf - Bezirk 3 | PC Kabel & Adapter gebraucht kaufen | eBay Kleinanzeigen
Corsair Premium 600W PCIe 5.0 / Gen 5 12VHPWR-Netzteilkabel – Passend für Typ-4-Netzteile über Zwei 8-Pin-PCIe-Anschlüsse – 12+4-Pin-Stecker – Mesh-Paracord-Ummantelung – Schwarz: Amazon.de: Computer & Zubehör
CORSAIR 12VHPWR 600W Cable Launched For GEFORCE RTX 40 Series