PC power supply – wattage, headroom and connectors

Where to get the numbers

The biggest power consumers in a computer are the graphics card and the processor. Their makers publish the power draw, but under different names:

Component	Maker’s figure	Example from the official specification
NVIDIA GeForce RTX 5070	Total Graphics Power	250 W, recommended PSU 650 W
NVIDIA GeForce RTX 5090	Total Graphics Power	575 W, recommended PSU 1000 W
AMD Radeon RX 9070 XT	Typical Board Power	304 W, minimum recommended PSU 750 W
AMD Ryzen 7 9700X	Default TDP	65 W
AMD Ryzen 9 9950X	Default TDP	170 W
Intel Core Ultra 9 285K	Processor Base / Max Turbo Power	125 W / 250 W

With processors, watch out for TDP. With AMD it is not the maximum power draw: for the AM5 socket, AMD clarified in 2022 that a TDP of 170 W comes with a power limit (PPT) of 230 W. Intel states the “Maximum Turbo Power” directly – 250 W for the Core Ultra 9 285K.

Why the graphics card maker recommends such a large PSU

For the RTX 5090, NVIDIA lists a TGP of 575 W but a recommended power supply of 1000 W. The difference is not all taken by the graphics card – the recommendation applies to the whole system. In a footnote, NVIDIA says the minimum is based on a PC with a Ryzen 9 9950X processor and that requirements may vary by configuration.

There are three reasons for headroom:

1. Short spikes. Graphics cards and processors draw more than their rated power for fractions of a second. The ATX 3.x standard therefore defines which short-term excursions a power supply must handle.
2. Everything else. Motherboard, memory, drives, fans, USB devices.
3. Efficiency and noise. A power supply running close to its maximum is louder and runs hotter.

Connectors matter as much as watts

A graphics card needs specific connectors. For the RTX 5090, NVIDIA lists two options: four 8-pin PCIe cables via the adapter supplied with the card, or one 600 W PCIe Gen 5 cable. For the RTX 5070, two 8-pin cables via the adapter or a 300 W cable will do. For the reference design of the RX 9070 XT, AMD lists two 8-pin connectors – specific partner cards may differ.

The 12V-2×6 connector was introduced by the ATX 3.1 and PCIe CEM 5.1 specifications as a revised version of the 12VHPWR connector. The cable has not changed; what changed are the pin lengths on the card side and the power signalling via the sense pins (up to 600 W).

How to go about it

Use the PSU calculator. Choose the processor and graphics card class, the number of drives and fans, and the calculator shows which numbers the result came from and how much headroom it added. If your graphics card maker states a higher recommended wattage, go with that.