Polymodding PSUs generally doesn't go nearly as well as motherboards.

Use good quality low ESR capacitors in PSUs. Try to match ESR as best as possible, but don't stress too much about it. There is a decent amount of tolerance in the PSU design.

canthearu wrote:

Polymodding PSUs generally doesn't go nearly as well as motherboards.

Use good quality low ESR capacitors in PSUs. Try to match ESR as best as possible, but don't stress too much about it. There is a decent amount of tolerance in the PSU design.

PSU filter caps usually don't require ultra low ESR caps like motherboards sometimes do, so replacement by polys is less beneficial as well.

retardware wrote:

Measurements were taken directly at load point (where the resistor/bulbs connection junction from). To make sure the fans do not […]
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Deunan wrote:

However if you get spikes like these with pure resistive load (like the 12V bulbs you have) then either something is broken, or the PSU was crap to begin with (poor design). It's best to measure that near the load as that is where you want clean power. Sometimes even the cable from the PSU to the load is inductive enough to clean up some HF noise.

Measurements were taken directly at load point (where the resistor/bulbs connection junction from).
To make sure the fans do not factor in, I'll modify the PSU tester so that it takes the fan supply from an external PSU.
If the spikes then still are there, they must come from the PSU I am trying to fix.

I did just that and the spikes seem now gone. So they might indeed have originated from the PSU tester fan and not from the PSU in question...

rasz_pl wrote:

old style car incandescent bulbs are great as makeshift load

I thought so too, but it turned out a bit differently:
when I turn on the both parallel 12V 50W bulbs that I intended to use for high load measuring, they are like a short when still cold. This appears to make the overcurrent protection trip and turn off the PSU, at least those which have that feature.
On PSU that do not have overcurrent protection, there is a big sag (5V to near 4V) until voltages have reached their correct values again.
So the bulbs seem to work fine indicating the presence of OCP, too.

I wonder, if I have a board with a short tantalum, a PSU without OCP will make better kaboom, inclusive burning up the boards traces.
So I guess the "OCP indicator" might be helpful detecting these PSU without OCP.

Edit:

canthearu wrote:

Polymodding PSUs generally doesn't go nearly as well as motherboards.
[...] There is a decent amount of tolerance in the PSU design.

Aww... now I know I did a bad thing.
But luckily it turned out the polymodding in this case apparently didn't do detrimental. Output is still in spec (<40mVpp on 5V, <60mVpp on 12V).