The NVIDIA GeForce RTX 3090 may have a 350 W TDP but it can consume nearly 60% more
So, the RTX 3090 Founders Edition has a 350 W TDP, which is 30 W higher than the TDP of the RTX 3080 and a whopping 130 W more than the TDP of the RTX 3070. Similarly, the TDP of the RTX 3090 Founders Edition is almost 35% higher than the TDP of the RTX 2080 Ti Founders Edition and 40% more than the reference spec card. Even the TITAN RTX only has a TDP of 280 W, so the RTX 3090 Founders Edition is one thirsty card.
However, the RTX 3090 can go much higher than 350 W. EMTEK has developed an RTX 3090 card with a 410 W TDP, for example, which requires 3x 8-pin power connectors. The GeForce RTX 3090 24GB XENON TURBOJET OC requires at least a 750 W power supply, which is what NVIDIA recommends for the RTX 3090 Founders Edition, too.
One owner of a Gigabyte RTX 3090 Gaming OC claims to have increased the power headroom of its card to 550 W, though. The Gaming OC has a reference design PCB and is a triple-fan design. vmanuelgm of Overclock.net states that they increased the card's power consumption from 390 W to 550 W by shunt modding. GamersNexus explains shunt mods in one of its hardware guides if you are unfamiliar with the process.
Upping the power consumption to 550 W has some performance benefits, as Videocardz has outlined. In saying that, 550 W is an awful lot of power to allow a card to consume, and there will be diminishing returns in this regard. Naturally, one would need more than a 750 W power supply in a system with a 550 W graphics card, too.