Last week, various outlets were reporting (incorrectly) that PCIe 4.0 would provide “at least 300W” through the slot. This would have been roughly equal to the power draw that a PCIe 3.0 GPU could provide with an extra six-pin and an extra eight-pin power connector, but do so all through the slot.
Later, the PCI-SIG contacted Tom's Hardware (and likely others) to say that this is not the case. The slot will still only provide 75W of power; any other power will still need to come from external connectors. The main advantage of the standard will be extra bandwidth, about double that of PCIe 3.0, not easing cable management or making it easier to design a graphics card (by making it harder to design a motherboard).