A brief explanation why
When attached to a motherboard's PCIe x16 slot, a card such as the GeForce RTX 4080 can draw up to 75W from the +3.3V and +12V rails (3.3V x 3A + 12V x 5.5A). This is the maximum amount specified by the PCI Express standard for a x16 slot (PCIe 4.0 and 5.0 spec). If a graphics card requires more power, it will typically have additional power connectors to supply the necessary energy.
Plugging a 6-pin PCIe power connector into the graphics card provides up to an additional 75W, and an 8-pin connector offers an additional 150W.
One of the key updates in the PCIe 5.0 specification includes the introduction of the 12VHPWR power connector, which can supply up to 600 watts of power through a single connector.
PCIe x4 and x8 cards can draw up to 25W from the motherboard's slot, while x1 cards are limited to 10W unless configured as a 'full-height' or 'high-power card' to pull the aforementioned 25W.