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 ...

2 SSDs and graphics cards. To be PCIe 4.0 compatible, several components on the motherboards are necessary, including PCIe 4.0 ready clock generator, lane switch, redriver, PCIe slots, and M.