I had a Corsair power supply with this feature. The system I built with it was quite flaky, but I could reproduce the failure and eventually debugged a 12V transient dropout (when running AVX workloads) that was the cause of the flakiness. The built-in monitoring didn't help at all; doesn't update frequently enough, and the computer crashed by the next USB polling cycle anyway. I used an oscilloscope.

I don't really have enough data to outright blame the power supply. I don't think I connected all of the 12V lines to the motherboard (power supply didn't come with enough cables), and I can't be sure that the motherboard was designed properly for a mildly-overclocked 6950X (VRM banks, capacitors near the CPU, etc.)

It was all enough of a pain that I will never buy another Corsair power supply. My current best practices involve only buying Seasonic power supplies, and connecting every possible "optional" power connector to the motherboard. If the PSU doesn't come with enough cables to do that, buy them separately. My current Threadripper motherboard has a 6-pin and 2 4-pin ATX12V connectors, and a Molex connector. Many are marked "optional" in the motherboard's instruction manual, but I have them connected anyway. Probably overkill. Great stability. Without having designed the system or the test scenario, skipping optional things sounds like the sort of thing that's going to cost you a lot of time at some random point in the future. Best to avoid, even if you look like an idiot to the EE that designed the board.

Corsair AXi and HXi series. They even got upstream kernel support: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...

Here is my output from lm-sensors

    $ sensors
    corsairpsu-hid-3-1
    Adapter: HID adapter
    v_in:        230.00 V  
    v_out +12v:   12.00 V  
    v_out +5v:     5.00 V  
    v_out +3.3v:   3.00 V  
    psu fan:        0 RPM
    vrm temp:     +49.0°C  
    case temp:    +40.0°C  
    power total:  96.00 W  
    power +12v:   80.00 W  
    power +5v:    16.00 W  
    power +3.3v:   8.00 W  
    curr in:          N/A  
    curr +12v:     6.00 A  
    curr +5v:      3.00 A  
    curr +3.3v:    2.00 A

Server PSUs support such communication (looks like this is PMBus protocol, variation of SMBus, which is variation of I²C). In servers it's connected to the BCM and usually allows to read input and output power, FAN speed, temperatures and status (good/bad). The BCM often records historical data, including peak power (in last 1h, 24h), etc.

After quick searching is looks there are people reading this info with a MCU [1]. But I think it would be hard to find such PSU in ATX form factor.

[1] https://github.com/sxjack/dps750tb_psu_i2c

Whenever I experience issues which are likely related to a power supply, it is much easier to drop in a known-good replacement than to spend time diagnosing the specific issues. Also better to remove a potentially faulty PSU before it damages much more expensive hardware.

The typical failure modes mean that it'll be marginal for a while, and should be able to give you information before it goes fully bad. Being able to have introspection before it goes fully bad is what I want, as I hope to have some data before it even makes it's way on to a bench.

The power clients (mainboard, GPUs, disk drives, etc) normally know they're getting pretty bad power from a PSU and filter it heavily to smooth it out. It'd be nice to know if the voltage is occasionally dropping and it's just being covered up by downstream caps that are over provisioned to just smooth out not fully rectified AC.

The data isn't necessarily collected. Many existing supplies use hardware counters or PWM modules to control the power output at a level very close to hardware.

In both of those cases there's a feedback loop setting the PWM dynamically. Even the error term of the PID or what have you would be super helpful.

There is no PID loop in the sense you mean. It's a hardware counter module that feeds a flip flop. There might be a free running ADC that is used to compare match against the counter module, or sometimes it's just a binary input like the AC signal zero crossing.

You don't need a CPU core to do this, and the older, cheaper parts do not necessarily have a CPU in them. There are even (iirc, very uncommon) designs with no digital logic save the switching.

IIRC, Corsair's AXi and HXi series power supplies -- basically, the really expensive ones! -- support PMBus (I2C).

The entry-level and lower-priced ones don't, AFAIK.