Hmm strange.
I can't help you further with that.
All I can say is that my TUSL2-C is working with modern EVGA 500 PSU.

What is the brand and model of your modern PSU?
Some of the cheapie / generic "modern" PSU's I've seen are just a tweaked ancient group-regulated design that doesn't do well with a heavy(er) load on the 5V rail and prefers a heavy 12V load only. I've also seen this happen on some not-s0-cheapo / non-generic modern PSUs too, though a lot more rarely. Either way, a Pentium II/3 board puts most of its load on the 5V rail (for the CPU), so that is likely making the 12V rail shoot too high and trip the PSU protections... or the 12V rail load is not large enough to sustain operation of the PSUs (some modern PSUs can be like that.)

It may be possible to "fool" your modern PSU by putting a 12V incandescent or halogen bulb on the 12V rail. One rated for 15-20 Watts should do. More may trip the OCP/S-C protection, particularly if it's a halogen type bulb.

momaka wrote on 2024-07-13, 15:10:

What is the brand and model of your modern PSU?
Some of the cheapie / generic "modern" PSU's I've seen are just a tweaked ancient group-regulated design that doesn't do well with a heavy(er) load on the 5V rail and prefers a heavy 12V load only. I've also seen this happen on some not-s0-cheapo / non-generic modern PSUs too, though a lot more rarely. Either way, a Pentium II/3 board puts most of its load on the 5V rail (for the CPU), so that is likely making the 12V rail shoot too high and trip the PSU protections... or the 12V rail load is not large enough to sustain operation of the PSUs (some modern PSUs can be like that.)

It may be possible to "fool" your modern PSU by putting a 12V incandescent or halogen bulb on the 12V rail. One rated for 15-20 Watts should do. More may trip the OCP/S-C protection, particularly if it's a halogen type bulb.

Loading the 12V rail on such a PSU with a few hard drives might be enough, as a test.

Getting a modern PSU that derives its 5V and 3.3V rails from its 12V using DC to DC converters AND still provides enough current on the those secondary rails might be an options. Luckily, Pentium 2/3 systems are not that power hungry.

momaka wrote on 2024-07-13, 15:10:

What is the brand and model of your modern PSU?

This is the one I'm using.

https://www.evga.com/products/product.aspx?pn=100-BR-0500-K1

Thanks for everyone’s response. The mystery is solved (kinda). I tried loading the modern PSU with multiple hard drives but no luck. I then borrowed another modern PSU from a friend and the TUSL2-C powered on perfectly. So there must be something weird going on with my modern PSU.

I once had this issue, reason I believe to be the cause is the low impedence of some components. I had 25-30 ohms on +5 and +3.3.
But the board worked perfectly fine.

Maybe some other component needs to kick in at some point but is too fast/slow and maybe the PSU is detecting it as a short? a power good not coming in when expected?
This is just a wild guess.

zuldan wrote on 2024-07-13, 08:42:

All the caps look good and the ESR meter was happy with them too.

if you tried in circuit, don't believe what was said.
motherboards are way much too complex circuitry too get an accurate esr reading in circuit. a lot of things can fool an esr meter, even a peak atlas can totally fail in circuit reading when it's too complex.
specially on all capacitors realted to chipset/cpu/vrm/ram.
i tried with a peak atlas 70 gold in circuit on an obviously bulged one : 0.60 ohm... it can't be true, and a very high capacity was reported (more than 10000 µF)

Tusl2 is not used 3.3volt of psu rail, only 5v
3.3volt is converted from 5v direct at board(dc-dc at right top corner)
And it's sucks- need psu with strong +5v rail