Monday, August 29th 2022
ATX 3.0 PSU Specification Loophole Lets Manufacturers Evade Stringent Excursion Tolerance Testing by Simply Excluding the 12+4 pin Connector
When testing recent high-end GPU launches such as the AMD Radeon RX 6950 XT graphics card, we observed some system reboots that caused due to power-draw spikes (technically known as "excursions"). This is when a graphics card, for a brief moment, draws more power than the connector is capable of supplying, triggering the PSU's electrical protections, and causing a reboot. The new ATX 3.0 specification for the next-generation of desktop PC power supplies enable PSUs with a high tolerance for excursions, and prescribes testing standards to ensure a PSU meets the ATX 3.0 spec. Aris Mpitziopoulos (crmaris) and Jon Gerow (Jonnyguru) discovered wording in the latest Intel ATX 3.0 specification that could make you pay closer attention to reviews of ATX 3.0-spec PSU, when they're out.
In a Hardware Busters article, Mpitziopoulos clears the confusion that the ATX 3.0 power supply specs by Intel and the PCI-Express 5.0 power specification by the PCI-SIG, are mutually-inclusive—they're not. An ATX 3.0 PSU is not required to include a 12+4 pin (or 16-pin) ATX 12VHPWR connector, whether or not their nameplate Wattage is above 450 W, which means it's subjected to passing less stressful transient-response tests, particularly the ability to deal with a 200% excursion for at least 100 µs.
The ATX 3.0 also introduces a feature called Alternative Low Power Mode (ALPM), which is hardware-level preparation for OS-level system low-power device states, such as Windows 10 Modern Standby and ChromeOS Lucid Sleep. The ATX 3.0 spec had prescribed certain new hold-up time requirements for PSUs offering ALPM, however it was discovered that these specs only apply to the 3.3 V rail, and not the all-important 12 V.
Put simply, the vagueness in Intel's specs allow the manufacturer of a cheap/mainstream PSU to claim ATX 3.0 readiness by excluding a 12VHPWR connector at any nameplate-Wattage, just so they can evade the steep transient-response testing required to include such a connector. It allows them to [over]compensate with a large number of conventional 150-Watt 8-pin PCIe connectors, and hope that people use cables included with their next-generation graphics cards that convert a number of PCIe connectors into a high-Wattage 12+4 pin connector.
Sources:
Hardware Busters, Igor's Lab
In a Hardware Busters article, Mpitziopoulos clears the confusion that the ATX 3.0 power supply specs by Intel and the PCI-Express 5.0 power specification by the PCI-SIG, are mutually-inclusive—they're not. An ATX 3.0 PSU is not required to include a 12+4 pin (or 16-pin) ATX 12VHPWR connector, whether or not their nameplate Wattage is above 450 W, which means it's subjected to passing less stressful transient-response tests, particularly the ability to deal with a 200% excursion for at least 100 µs.
23 Comments on ATX 3.0 PSU Specification Loophole Lets Manufacturers Evade Stringent Excursion Tolerance Testing by Simply Excluding the 12+4 pin Connector
Meanwhile the rest of us wont have issues because we still use the 24 pin connector, like the rest of the AIB industry.
Something tells me the industry is gonna stick with the usual 8 pin for awhile yet.
Does anyone understand why certain standards setting bodies include vague requirements and/or loopholes? I mean look at the USB nightmare. USB3.0, USB 3.1, USB 3.2 Gen1/Gen2/Gen2x2. What the actual F. Why not just simple labeling: USB 3 (5, 10, 20 Gbps)?
And in regards to power supplies, do some of the member companies like Nvidia, PSU manufacturers etc., have too much sway into the language of the standards... so as to not negatively impact future sales?
I can't understand why some PSUs that don't have to undergo the stringent testing requirements are able to be considered "ATX3.0"?
What's the functional difference between existing ATX2.x PSUs (e.g., Corsair RMx1000) and an "ATX3.0" PSU (that lacks the 12+4 pin) connector?
Some older PSUs did shutdown with even slightest overload.
Talking about high end gpu's and referring to a lower powered 450w psu is pretty funny comparison to me frankly :kookoo:
Not to mention most spec's say 850w recommended.
L. Finger
Scream and cry all you want, but the 16 pin is going to be the new standard, just like USB-C replacing USB-A.
That is one cheap way to get rid of the spikes.
A 1/4F would be enough for a 1500W PSU, but even that would trip the inrush current on charge. :D