PSU Manufacturers Can Skirt ATX 3.0 Tolerance Testing By Skipping This Feature

hero PCIe 50 connector
Just like the PCIe 5.0 specification, Intel's ATX 3.0 spec introduces a number of new measures intended to support upcoming graphics cards with extremely high power draw. Among those are some stringent tests that products have to pass before the manufacturers can call them "ATX 3.0"-compliant. Unfortunately, vague language in Intel's documentation means that vendors can opt to avoid the tests by skipping the 12VHPWR connector.

That connector, as regular readers will recall, is also known as "the PCIe 5.0 power connector". It's the 12+4-pin power connector that will likely appear on the upcoming GPUs from AMD and NVIDIA; a version of it without the 4-pin add-on already appears on NVIDIA's extant RTX 3000-series Ampere GPUs.

power excursion testing
Source: Intel ATX 3.0 specification, via Hardware Busters

Under the ATX 3.0 specification, power supplies with the 12VHPWR connector must be able to handle up to 200% of their rated power for at least 100μs, 180% for 1ms, 160% for 10ms, and 120% for 100ms. This type of overload capacity is specifically intended to handle the intense "transient loads" that modern graphics cards can create. The technical term for these normally brief spikes is "excursions."

Now, elsewhere in the documentation, Intel clearly states that power supplies with rated load over 450 watts must include the 12VHPWR connector. As you can see in the above chart, the spec also provides for power supplies without said connector. What gives, Intel?

optional power connector is optional
Source: Intel ATX 3.0 specification, via Hardware Busters

It was confusing enough to Hardware Busters' Aris Mpitziopoulos that he reached out to Jon Gerow (better known as Jonnyguru, now working for Corsair). After some discussion, the two of them consulted with Intel. As it turns out, no—power supplies rated for 450W and higher are not actually required to have 12VHPWR connectors. However, only units that do have the connectors are required to pass the more stringent excursion testing.

What this means in practice is that manufacturers can skip the fancy new PCIe 5.0 connector and thus cheap out on their units' ability to handle transient spikes from power-thirsty graphics cards. These spikes can be quite extreme; various outlets have recorded sub-millisecond spikes of over 800 watts from the GeForce RTX 3090 Ti. Remember that this is in addition to whatever the rest of your system is drawing.

pcie 50 12vhpwr
Probably don't buy it if it doesn't have one of these. But we're not the boss of you.

Whether this is actually a problem ultimately depends on your purchasing habits. If you're buying a new graphics card and then using a creaky old power supply to drive it, may whatever God you choose help you. Likewise, if you're buying a graphics card with a PCIe 5.0 connector on it and then using adapters to connect it to two, three, or four old-school eight-pin PCIe power connectors on the power supply side, you'd better be sure that power supply can handle the load.

The safer bet, if you're buying a brand-new graphics card this holiday season, is to pick up a new ATX 3.0 power supply. Models that come with the 12VHPWR connector won't be cheap, but thanks to the high standards of the ATX 3.0 spec, they should be capable of more reliably handling the power demands of upcoming GPUs. Of course, this does mean consumers need to verify if the 12VHPWR connector is, in fact, included. The ATX 3.0 certification is not a guarantee on its own.