To get an idea, add the TDP of all the power hungry components:

Athlon 64 X2 4400+: 110 W (12V)
X850 XT Platinum: 67 W (mainly 12V)
9800 Pro AGP: 47 W (mainly 12V)

That amounts to 214W (18A) on the 12V rail. That of course is when everything in your system runs at full load, including both graphics cards, which likely won't happen in practice. But these older cards draw significant power even when they're not doing anything, so you should still assume 70-80% of their combined power.

The 5V and 3.3V power needed should be negligible for your system, so any PSU would be good enough for those.

I would also look for a PSU where the 24-pin ATX connector can be truly separated and not just bent apart. That sometimes causes problems on older boards when the 4-pin connector is blocked by a large inductor or capacitor near the ATX connector.

Some PSUs split their 12V current limit into two or more rails, so if it says something like 12A + 12A, that would also work for your system. You would need at least 10A on one of the rails for your CPU (110W / 12V = 9.2A).

asdf53 wrote on 2025-11-18, 06:21:

To get an idea, add the TDP of all the power hungry components: […]
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To get an idea, add the TDP of all the power hungry components:

Athlon 64 X2 4400+: 110 W (12V)
X850 XT Platinum: 67 W (mainly 12V)
9800 Pro AGP: 47 W (mainly 12V)

That amounts to 214W (18A) on the 12V rail. That of course is when everything in your system runs at full load, including both graphics cards, which likely won't happen in practice. But these older cards draw significant power even when they're not doing anything, so you should still assume 70-80% of their combined power.

The 5V and 3.3V power needed should be negligible for your system, so any PSU would be good enough for those.

I would also look for a PSU where the 24-pin ATX connector can be truly separated and not just bent apart. That sometimes causes problems on older boards when the 4-pin connector is blocked by a large inductor or capacitor near the ATX connector.

Some PSUs split their 12V current limit into two or more rails, so if it says something like 12A + 12A, that would also work for your system. You would need at least 10A on one of the rails for your CPU (110W / 12V = 9.2A).

The statement on the 9800 Pro does not hold true. It does pull the majority of its Power from the 5V and 3.3V rails: https://tehsiggi.github.io/agp-power-monitor/ … 00pro_128_hynix

Furthermore, total power consumption under max load can go up 70W for 9800Pro

tehsiggi wrote on 2025-11-18, 07:58:

asdf53 wrote on 2025-11-18, 06:21:

To get an idea, add the TDP of all the power hungry components: […]
Show full quote

To get an idea, add the TDP of all the power hungry components:

Athlon 64 X2 4400+: 110 W (12V)
X850 XT Platinum: 67 W (mainly 12V)
9800 Pro AGP: 47 W (mainly 12V)

That amounts to 214W (18A) on the 12V rail. That of course is when everything in your system runs at full load, including both graphics cards, which likely won't happen in practice. But these older cards draw significant power even when they're not doing anything, so you should still assume 70-80% of their combined power.

The 5V and 3.3V power needed should be negligible for your system, so any PSU would be good enough for those.

I would also look for a PSU where the 24-pin ATX connector can be truly separated and not just bent apart. That sometimes causes problems on older boards when the 4-pin connector is blocked by a large inductor or capacitor near the ATX connector.

Some PSUs split their 12V current limit into two or more rails, so if it says something like 12A + 12A, that would also work for your system. You would need at least 10A on one of the rails for your CPU (110W / 12V = 9.2A).

The statement on the 9800 Pro does not hold true. It does pull the majority of its Power from the 5V and 3.3V rails: https://tehsiggi.github.io/agp-power-monitor/ … 00pro_128_hynix

Furthermore, total power consumption under max load can go up 70W for 9800Pro

Thank you for the measurements, always great to have that and not mere assumptions. I assumed 12V because that's what high power cards usually use. Now even if the relative draw for 5V is higher than 12V, it still wouldn't be an awful lot in absolute terms as long as you use 12V for the CPU.

On the other hand, looking at your measurements (Radeon = 30W, and a similar X800XT = 20W), my claim that just any PSU would be good enough for 5V doesn't hold true, considering that some of the bare minimum ones top out at 12A. So better to have 15A on the 5V rail to be on the safe side, assuming the worst case of running both cards at maximum power. Fortunately, PSUs with 15A and 20A shouldn't be hard to find.

The big difference between "old" and "modern" PSUs is that, based off their circuitry, their primary regulation lies on a different rail. Old ones focused on 5V/3.3V with the 12V tailing those. More modern ones (not the DC/DC world we live in today) tend to regulate for the 12V rail and having the other tailing it.

So yeah, having a PSU with at least 15A on 5V and 3.3V would be good, but it's not a guarantee that a 9800Pro might be happy. If the PSUs regulation is bad on those rails, it might cause trouble.

The X800XT from my test you can keep out of the picture, as it is an AGP variant and PCIe has only 12V and 3.3V at the slot + 12V on the 6pin.

As an owner of a 939Dual-SATA2, I can tell you that this motherboard's Northbridge is somewhat on the more power-hungry side, drawing probably close to 15 or 20 Watts total under load (at least judging by how hot the cooler gets on it, even with me adding a fan to blow air on it), most of which comes from a buck regulator supplied by the 5V rail. Meanwhile, the 3.3V rail supplies the RAM and also parts of the NB, plus the entire SB.

Given that you want to use a Radeon 9800 Pro with it (which is a 5V and 3.3V -heavy video card), I too would suggest to make sure your PSU is capable of providing at least 18 Amps on the 5V rail and probably something like 12-15 Amps on the 3.3V rail, just to be relatively safe. That said, you don't need to look for an old, 5V-heavy PSU... just a modern_ish) one that can do the above currents on the 3.3V and 5V rails. Other than that, given that your CPU and X850 will likely draw from the 12V rail and the 9800 Pro from the 3.3V+5V rails, this should be a pretty balanced system in terms of 3.3-5-12V loads.

And additional note for the 939Dual-SATA2: make sure to keep the Northbridge and Southbridge well-cooled on your board, as I've seen these fail with higher ambient temperatures, like my 1st 939Dual-SATA2 did (SB failure due to overheating, and now my onboard sound is dead + onboard LAN and SATA/SATA2 ports are flakey... and it's not a caps issue, because I've recapped it too.) Luckily, my 2nd one has been spared that fate... or so it seems for now (haven't done a built with it yet.)