A brief explanation why
When installed in a motherboard's PCIe x16 slot, a graphics card such as the GeForce RTX 5080 can draw up to 75 watts of power directly from the slot. This power comes from the motherboard's +3.3V and +12V rails (3.3V × 3A + 12V × 5.5A), which is the maximum defined by the PCI Express base specification for a x16 slot (this limit has remained consistent across PCIe 1.0 through PCIe 5.0).
Without any additional power connectors attached, this 75W is the total available power to the graphics card. Entry-level or low-power GPUs may operate entirely within this limit. However, most modern mid-range and high-end GPUs require significantly more power to achieve their full performance potential.
To provide this extra power, graphics cards typically include one or more supplementary PCIe power connectors:
- A 6-pin PCIe connector can supply up to an additional 75W.
- An 8-pin PCIe connector can supply up to 150W.
- The newer and controversial 12VHPWR connector (introduced alongside PCIe CEM 5.0 and ATX 3.0 power supply standards) can deliver up to 600W through a single cable. This connector is increasingly common on high-end GPUs.
For other PCIe card types:
- PCIe x4 and x8 cards can draw up to 25W from the motherboard slot.
- PCIe x1 cards are limited to 10W, unless configured as a "full-height" or "high-power" card, in which case they can also draw up to 25W.