Our First Foray Into ATX 3.0 PSU Testing: A High Hurdle to Clear

In light of the new ATX 3.0 standard, we took a shot at adding power excursion compliance testing into our articles. Given that this is the big addition to the ATX 3.0 specification– and indeed its very reason for being – it's where we would like to see if PSUs are truly living up to the very high standards set by the new specification.

Unfortunately, the testing requirements of the new standard have proven too high for our equipment - and that of the majority of small laboratories - to meet. The power excursion specifications suggest electrical current-to-time figures that are extremely short. For example, taking the MEG Ai1300P of this review into consideration, for the single case of the 200% power excursion testing, we would need to test that it can handle 2600 Watts for 0.1 ms. Assuming a starting load of about 800 Watts and 65 A on the 12 V rail, the 12 V load would have to get up to 215 A and back down to 65 A within 0.1 ms. Furthermore, according to Intel's testing guide, this would have to continue for at least a minute, which means at least five hundred cycles in this scenario.

In an ideal world, we would just enter the current and time figures into the software and our electronic loads would run the test, instantly getting the load up to 215 A for 0.1 ms and then immediately back down to 65 A for 1.9 ms, according to the guide's requirements.

In the real world, however, there is no such thing as "instantly". Electronic loads, like any other device that is bound by the laws of physics, require time to react. The speed at which an electronic load can increase its amperage is called Ramp (or Slew) Rate and our larger loads have an ideal Slew Rate of 0.5 A/μS. Assuming that they operate linearly and exactly as specified, which no electronic load does for a variety of reasons, our two primary electronic loads in parallel would require at least 0.15 ms (150 μS) just to get the load up at 215 A. They would also require time, albeit less than half of it, to get the load back down to 65 A. When the test dictates a test time of 0.1 ms and the testing equipment requires at least twice that much time just to react, it goes without saying that testing results are highly unreliable.

Nevertheless, we took a shot at testing the power excursion capabilities of the MSI MEG Ai1300P PCIE and of the few ATX 3.0 compliant units that we currently have available. We took two approaches: one by assuming that our electronic loads are "ideal" and programmed the exact duty cycle figures that Intel dictates in their guide, and one by trying to take into account the real slew rate times of our loads and calculate the RMS equivalent duty cycle.

Both of our approaches ultimately failed, as all of the PSUs we currently have available would shut down at most tests above 120% power excursion - therefore we need not worry about our loads being insufficient to test the MEG Ai1300P at 200% excursion (we are also currently limited to 2400 Watts on the 12V line). Theoretically, testing with the RMS-equivalent duty cycle times should work and the PSUs should not be shutting down, yet we cannot claim that the units are not technically capable of meeting their specifications when our equipment is not meant to be running such tests.

Intel requires the PSUs to have a slew rate of at least 5 A/μS, so an electronic load must be at least as fast as that figure to be able to perform ATX 3.0 compliance testing. From a professional's point of view, proper testing would require the testing equipment to be at least 30% faster than the absolute minimum required. This requires a highly advanced (and expensive) electronic load with multiple modules, like the Chroma Mainframe and High-Speed modules Intel themselves is using, which has a total slew rate of 8 A/μS and it would need only 0.02 ms to get the load from 65 A all the way up to 215 A - and that still is 20% of the test's required 0.1 ms time in our example, a figure that many experts would find far too great for precise measurements.

The MSI MEG Ai1300P PCIE5 1300W : Inside & Out Cold Test Results (~22°C Ambient)
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  • flyingpants265 - Wednesday, December 14, 2022 - link

    The plug thing is really overblown IMO, it could have happened to anyone. The important thing is
    1. Did they fix it, and
    2. Did they replace people's burnt computers?
    The plug should fit better. Larger and longer pins means more contact area... Need better fitment and tolerances to slide in and click properly each time. Also, the sensing pins are probably unnecessary. Just have an optional 450w bios.
  • TheinsanegamerN - Thursday, December 8, 2022 - link

    if you cant tell when its actually plugged in all the way, thats a pretty major issue.

    None of this is a poroblem with the 8 pin, you notice.....
  • NextGen_Gamer - Thursday, December 8, 2022 - link

    Yeah, I have not seen a 12VHPWR cable personally yet, but from what I have read, it just doesn't seem to "snap" in quite as tight as the current 8-pin PCI-E connectors. Which means even if you know what you are doing as a PC builder, you might not get it fully inserted. I also have to wonder, with the only two GPUs shipping that use being MASSIVE 3-slot and higher than normal height, that maybe NVIDIA should have provided a right-angle connector out of the box. Since because of where the 12VHPR connector is placed, you really have to bend it as it is hitting the side panel immediately. A right-angle connector would alleviate that stress, and might have been able to be inserted fully a lot easier.
  • tamalero - Thursday, December 8, 2022 - link

    Just installed my 4090 and I can tell you that you're right. That thing just doesn't snap nor holds itself like the PCIE connectors.
    I had no idea if it was fully connected or not. and I was worried I would start to bend the connector from the PCB of the card as the connector is very hard to insert.
  • DanNeely - Friday, December 9, 2022 - link

    I don't have one; but from coverage I've seen elsewhere, while the cable doesn't have a satisfying mechanical snap and audible click when inserted a strait pull and wiggle test will quickly dislodge an incompletely inserted cable without disturbing one that is in all the way. It's also recommended to plug power into the card before inserting it into the case so you've got more room to manipulate the wire and to inspect it's insertion.
  • flyingpants265 - Wednesday, December 14, 2022 - link

    Cables shouldn't be a thing anymore anyway. Apple's Mac Pro and the stadia devkit don't even use cables at all. Instead of "hiding" them, just eliminate them completely.
    But yeah, for 600W GPUs, you probably want a right-angle connector.
  • evilspoons - Thursday, December 8, 2022 - link

    Yeah, if you plugged this power supply's 12VHPWR cable in halfway as well I'm sure it would melt just as easily. The root issue is it's not easy to tell if it's latched and the sense signals that detect proper connection can do so without the connector actually latching.
  • Techten - Tuesday, December 13, 2022 - link

    I have the 850 Watt version of this PSU, and I had to gently create a curve in the 12VHPWR cable to get it in the RTX 4080 using a Corsair 4000D Airflow. I took my time over 5 minutes creating a soft curve and leaving at least 2 inches out of the card with out bending. The Cable was very stiff. There was a satisfying click sound once placed in the 4080 and you could easily see that it was flush with the female adapter of the card.
  • scottj - Thursday, December 8, 2022 - link

    Not sure about the Gaming Intelligence thing, but they could at least use a modern USB connector.
  • shabby - Saturday, December 10, 2022 - link

    At least its not a usb-b port 😂

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