Not unheard of...even on some of the so-called 'better' units. Both my Abit SlotKET !!! and my QDI s370 (V5.1) support upto 3.5V

There is a whole flock of slotkets that 'officially' support up to 3.5v:
Abit SlotKET III ver 1.0
Fastfame 370SP rev 1.0
Fastfame 370SP rev 2.0
Freeway Gigabyte FW-S370 rev 1.0
Gigabyte GA-6R7 Pro rev 2.0
Iwill Slocket II ver 1.0
Iwill Slocket II ver 1.1
Iwill Slocket II ver 1.2
Iwill Slocket II ver 2.0
Luckystar S9 / Image World Turbo-370 Card rev 1.1
Luckystar S9 / Image World Turbo-370 Card rev 1.2
Powerleap PL-PII
Powerleap PL-PII 433
Powerleap PL-iP3 ver 2
QDI 370 CPU Card 5.0 (S5.1)
Shuttle 370 CPU Card rev 3.2
Soltek SL-02A C-tune J rev 4.5
Soltek SL-02A C-tune rev 4.0
Soltek SL-02A++ rev 4.5
Soyo Pll CPU Card rev 1.0
This list is not complete and there are slotkets, like the MSI 6905 Master, that can most likely be set to 3.5v via undocumented settings.

The slockte only configures the VID signal on the slot. The voltages for each VID setting are specified by Intel. You can set any slocket with VID0-4 pins to all of those voltages regardless of wether it's documented and described on the silkscreen or not. This slocket is completely passive in that regard.

Yes. As far as I get it you can configure any slotket with 5x VID jumpers for the full range of 1.3 volt - 3.5 volt (of course dependant on the motherboard being able to cover that range). For this particular slotker it would then look like this (blue = 'undocumented'):

(edit: error in jpg corrected)

So is the sense of 'A' inverted from the rest? I suppose it has a different purpose, doubling the multiplier of B-E. Drawing out the full table with 2-3 as a '1' and 1-2 as a '0', but the other way around for column A, gives a nice binary count from 1.3V=00000 to 3.5V=11111.
I wonder what setting them all to 1-2 would do? A second way of setting 2.0V?

[I think there's one typo in your table, for the 2.0V line, I think D should be 2-3.]

Yes, thanks - the error is corrected.
The 'A' column corresponds with VID4 in the specsheets of pwm controllers like as in the attached example - page 7.
There are 2x 16 settings for the 2 groups above and below 2.05/2.1 volt

That's interesting. So the jumpers are simply requesting the voltage from the motherboard. Is this passed directly to the PWM controller or does BIOS get involved?

I'm looking to swap out the PWM controller on my ASUS P2B which can only be configured to 1.8V via slocket and this corresponds with the minimum voltage that the PWM controller can provide. The assumption being that swapping the controller chip is enough to overcome this limitation.

Kahenraz wrote on 2021-09-10, 17:45:

That's interesting. So the jumpers are simply requesting the voltage from the motherboard. Is this passed directly to the PWM controller or does BIOS get involved?

I'm looking to swap out the PWM controller on my ASUS P2B which can only be configured to 1.8V via slocket and this corresponds with the minimum voltage that the PWM controller can provide. The assumption being that swapping the controller chip is enough to overcome this limitation.

The swap should work. After you perform the swap, CPU voltage can be measured at a MOSFET near the VRM - it's the voltage between the MOSFET's tab and ground.

Stick a P133 on there and see what happens.