You probably want to keep things the way they are, it is quite likely all that extra capacitance will appear as a big enough short on startup that the VRM enters and stays in protection.

if the capacitors are in parallel then you can replace two 1500 with one 3300

Tiido wrote on 2023-08-11, 21:24:

You probably want to keep things the way they are, it is quite likely all that extra capacitance will appear as a big enough short on startup that the VRM enters and stays in protection.

Yeah, I also thought that all that extra capacitance may overload the VRM. 🙁

weedeewee wrote on 2023-08-11, 21:32:

if the capacitors are in parallel then you can replace two 1500 with one 3300

True, the caps are in parallel but I'd like not to change the mobo appearance.

So I guess, I'll be looking for 20 caps of 1500uF of the same size. The problem is that I rarely see such caps on a donor boards. 🙁

You can use half as many, although ESR and ESL are improved with more smaller parts compared to less and larger ones. The machine is unlikely to have any problem with half as many 3300µF ones vs all 1500µF ones.

If the 3300µF/16V caps really do fit in the places of the original 1500µF / 6.3V types, the 3300µF caps are either of poor quality or/and have too high ESR.
Can you provide the manuf. / series or a picture?

By and large, it is not the capacitance that matters, but the allowed current through the capacitors. Well, the ESR, as without it.
If the 3300 uF capacitor has a ESR and the allowable current is two times better than that of 1500, then you can set 1 instead of 2.

Zerthimon wrote on 2023-08-11, 21:51:

The problem is that I rarely see such caps on a donor boards. 🙁

So use the right donor.

Zerthimon wrote on 2023-08-11, 21:51:

weedeewee wrote on 2023-08-11, 21:32:

if the capacitors are in parallel then you can replace two 1500 with one 3300

True, the caps are in parallel but I'd like not to change the mobo appearance.

What "appearance"? Even the manufacturers like Gigabyte used this "trick" to spare some parts from their motherboards 20 years ago. I have one PIII board with half of capacitor's pads on main lines to CPU unpopulated. They're paired in parallel with pads with soldered 3300 mF caps. The manufacturer did the same - used one 3300 uF capacitor instead of two 1500 or 1800 uF.

majestyk wrote on 2023-08-12, 05:34:

If the 3300µF/16V caps really do fit in the places of the original 1500µF / 6.3V types, the 3300µF caps are either of poor quality or/and have too high ESR.
Can you provide the manuf. / series or a picture?

Capacitors were somewhat bulkier in late 20th century and shrank a bit at the beginning of this one.

BitWrangler wrote on 2023-08-12, 12:03:

majestyk wrote on 2023-08-12, 05:34:

If the 3300µF/16V caps really do fit in the places of the original 1500µF / 6.3V types, the 3300µF caps are either of poor quality or/and have too high ESR.
Can you provide the manuf. / series or a picture?

Capacitors were somewhat bulkier in late 20th century and shrank a bit at the beginning of this one.

It depends, physics still apply. A good low ESR capacitor for higher ripple current 3300µF 16 V still measures 16mm x 22mm:
https://www.digikey.com/en/products/detail/ru … wWUQA0xsQBdAXyA

I doubt the original 1500µF 6.3V were that large...

There exist - of courrse - far smaller ones with 3300µF / 16V, but they fail regarding lifetime and/or ESR and/or ripple current.

majestyk wrote on 2023-08-12, 19:49:

It depends, physics still apply. A good low ESR capacitor for higher ripple current 3300µF 16 V still measures 16mm x 22mm: htt […]
Show full quote

It depends, physics still apply. A good low ESR capacitor for higher ripple current 3300µF 16 V still measures 16mm x 22mm:
https://www.digikey.com/en/products/detail/ru … wWUQA0xsQBdAXyA

I doubt the original 1500µF 6.3V were that large...

There exist - of courrse - far smaller ones with 3300µF / 16V, but they fail regarding lifetime and/or ESR and/or ripple current.

There is no strict standard dimensions for capacitors with equal capacitance rated for same voltage. Even today some caps are "wider", others are "thinner" or "shorter"/"longer". Also dimensions varies between manufacturers/vendors. And as it was already mentioned even electrolytic caps "evolve" and somehow become "smaller" (especially those from respected brands).

majestyk wrote on 2023-08-12, 05:34:

If the 3300µF/16V caps really do fit in the places of the original 1500µF / 6.3V types, the 3300µF caps are either of poor quality or/and have too high ESR.
Can you provide the manuf. / series or a picture?

I wanted to replace these

with these

Edit: the rubies are 6.3V, updated the OP.

possibly applicable datasheets ?

I don't get the source of the problem.
Just buy some low esr caps with correct capacity and voltage.
1500uF/6,3V caps are so ridiculously cheep that using some used but higher capacity ones is pure madness 😀

Zerthimon wrote on 2023-08-13, 12:04:

I wanted to replace these
with these

To be honest, it looks like a desire to replace some 20-year-old capacitors of unknown condition with other 20-year-old ones.

shevalier wrote on 2023-08-13, 17:54:

To be honest, it looks like a desire to replace some 20-year-old capacitors of unknown condition with other 20-year-old ones.

Was about to post the same. Those MBZs are capacitors from the late 2000s. At best. Even if those caps are unused, they most likely are already degraded badly.

I don't understand why OP wants to do this, because datasheets are available for the originals and he could just find matching ones looking at the capacitance and voltage values, ripple current and ESR and order new matching capacitors. If similar caps aren't available anymore, then polymers should do the trick. Polymers of course change the look somewhat, but I'd choose changed look over the other option which is having an unreliable or non-working MB.

I can assure you that the worst low ESR capacitors now have better quality that those shown in the picture 😀

I got my answer for the question if doubling capacitance is a good or bad thing. So it is what I thought it is. Thanks everyone.