Not sure, but I have a similar story. Few months back, I sold a perfectly working HIS IceQ3 3850 AGP, but the buyer said the card was DOA. Even showed me a private YT video.

So I took it back and paid for all the shipping costs and customs, other side of the world ffs. Tried it in my test rig and works perfectly fine. Frustrating...
Older 550 Watt (Global Win?) psu with correct connectors.
Haven't tried a modern PSU with the card, sorry.

I'm completely guessing here, but it seems most logical to me that the issue might have something to do with the Power Good (PG) signal of the PSU. The PG signal of the PSU (on the 20/24-pin ATX connector) tell the motherboard (and rest of the hardware through the motherboard) when the PSU power rails are all fully up and running. Perhaps the old PSUs take a longer time (or shorter?) for the PG signal to appear, whereas with the new ones it's the opposite.
I imagine that if the PG signal takes too long on the new PSU, maybe that somehow makes the video card "time out" as the motherboard is still initializing / in reset mode. Or maybe it's the other way around?? - The PG is too quick, making the MB POST very fast, while the GPU is still not ready / initializing, thus making the MB "time out" the device on AGP slot.

If you have one of those cheap LCD PSU testers that measure the PG signal delay, perhaps that might reveal a difference between the new and old PSUs. I do wonder how accurate the measurement is of those cheap PSU testers, though. An oscilloscope would probably be the more accurate way to go.

I'm glad you brought up this issue, though. Makes me wonder if I have skipped and/or mislabeled any GPUs as non-working before due to this. I mostly use old and self-rebuilt PSUs, though. But for the really high-power GPUs (R9 280/290/380 and etc.) I use a relatively modern Thermaltake M850W PSU, which I've never though or tried to measure how its PG line acts. IIRC, I did have one HP OEM system refuse to POST with it consistently while it had no problems POSTing with just about every other old rebuilt PSU I threw at it. FWIW, my Thermaltake M850W is based on the CWT PUQ platform, IIRC. Corsair CX750M (another PSU I have) is also based on the same CWT platform... but I didn't test that one on the HP machine, since the CX750M I have is still a WIP (and a very looong workin-in-progress, if I may add.)

No idea why it happens, but HIS 3850 AGPs are definitely very picky with their PSUs. The only PSU that works with my card is a 2008 server PSU that I have attached with several PCIE power adapters.
On other PSUs, the card doesn't get any GPU or memory voltage. Which means, one of the major controllers doesn't give out the Power Good signal required. Why - again, don't know.

momaka wrote on 2024-07-13, 16:28:

I'm completely guessing here, but it seems most logical to me that the issue might have something to do with the Power Good (PG) signal of the PSU...

If you have one of those cheap LCD PSU testers that measure the PG signal delay, perhaps that might reveal a difference between the new and old PSUs. I do wonder how accurate the measurement is of those cheap PSU testers, though. An oscilloscope would probably be the more accurate way to go.

Nope, it isn't the Power Good signal. I've tested in the meantime all the PSUs I have (both old and new) and they all have the PG signal between 240 and 300 ms, which is well within ATX specs (100-500 ms). I am giving up temporarily on upgrading the PSU.

At least until someone in the forum, who has a working combination of both the HIS 3850 AGP and a new modern PSU, finds this thread and posts the model of his PSU. Thank you all for your contribution.

Older PSUs, like your Seasonic and OCZ, might have looser tolerances on their voltage outputs. This could be providing the HIS card with slightly more wiggle room on power delivery, which it might need due to aging components or manufacturing variations.
Modern PSUs tend to have stricter voltage regulations, which could be causing the HIS card to malfunction if it's slightly outside the acceptable power range.
You could try to see if your newer PSUs allow some level of voltage control, try very slightly increasing the voltage output on the 12V rail. Do this with extreme caution and only if the PSU allows it. A small increase might provide the headroom the card needs.

get a budget PSU and test, the budget models still use group regulation like the old days see if that helps.