In general, more is better.
My Athlon 1400 is powered by a Sweex 650W PSU with a radial fan.

It's a pretty cheap and simple PSU, and basically only has one rail, so all the 650W goes to where it matters for the Athlon.
I don't think any modern ATX PSUs would cut it.

They still list a variation of it on their website: http://www.sweex.com/en/beeld-geluid/ps040/
So I wonder if they're still basically the same spec as mine, and if you can still get them.
The figures look good anyway:
+ 3.3 V : 32 Amp, + 5 V : 30 Amp, +12 V1 : 17 Amp, +12 V2 : 16 Amp, -12 V : 0.3 Amp, + 5 Vsb: 2 Amp Peak: 2.5 Amp

Phil just did a video yesterday about this very topic:

https://www.youtube.com/watch?v=efK7mw8eYiE

Scali wrote:

In general, more is better. My Athlon 1400 is powered by a Sweex 650W PSU with a radial fan. https://www.webhallen.com/image/pro […]
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In general, more is better.
My Athlon 1400 is powered by a Sweex 650W PSU with a radial fan.

It's a pretty cheap and simple PSU, and basically only has one rail, so all the 650W goes to where it matters for the Athlon.
I don't think any modern ATX PSUs would cut it.

They still list a variation of it on their website: http://www.sweex.com/en/beeld-geluid/ps040/
So I wonder if they're still basically the same spec as mine, and if you can still get them.
The figures look good anyway:
+ 3.3 V : 32 Amp, + 5 V : 30 Amp, +12 V1 : 17 Amp, +12 V2 : 16 Amp, -12 V : 0.3 Amp, + 5 Vsb: 2 Amp Peak: 2.5 Amp

If in doubt, open it up. You don't want to be drawing 30A on a 5V rail which has been costed down to within a millimeter of it's life. "Creative" engineering fixes like deleting output filters or substituting for safety rated parts can present a hazard to your hardware, or, in the worst cases, to your life and property.

I found some test and teardown data on this Sweex supply*. It appears to be more or less complete (except for a TVS device) as far as both input and output filtering and provides good ripple suppression on all three rails, but regulation at 500W and beyond begins to look increasingly suspect.
* https://translate.google.ca/translate?hl=en&s … 50_w%2F49326%2F

Given the dated topology used and the heavy crossloading required for typical ATXv1.3 high wattage loads of the Athlon era, I question whether regulation will be maintained in practice. Furthermore, the more restrictive fan configuration and suspect choice of capacitors (both brand and temperature rating) makes me question the longevity of this supply as well.

The brand Sweex is pretty much a giveaway that it's not going to be a high-end product. It's a cheap budget brand. Having said that, at the time I bought it, this was their highest-end model.
My logic was simple: The Thunderbird 1400 system would need a power supply in the range of 350-400W. So a high-end 400W PSU would be able to feed it.
This Sweex is well over-specced for that system, so even though it may be low-end, it would never be stressed much, and as such, it should work fine.

And it did. I've had it for over 10 years and it still works fine. Which is more than I can say of any previous PSU that it burnt through.

As for the fan, it's a radial fan as opposed to an axial one. I've never seen any other PSU with a radial fan, but this fan pushes out a lot of air.
It fit in nicely with the Silverado CPU cooler I use on the CPU, which has two radial fans on it.

Edit: the one I have appears to be more powerful on the 5v rail than the unit they tested:

Those are some serious specs on the 3.3v and 5v lines.
And it lists one 12v spec, which is why I assume it is a one-rail PSU, where the newer one seems to have two rails.