Your Athlon will draw power from the main 20 pin connector. I would recommend PSU that has strong 3.3V+5V rail, comparable to your old PSU. You won't be using the 4 pin 12V connector from your new PSU. If it comes with SATA connector you can use an adapter.

To put it into perspective my old Chill 510W PSU has the following rating - 3.3V - 33A, 5V - 45A, 12V - 25A. Power output is 330W on 3.3V+5V and 480W on 3.3V+5V+12V. Of course you don't need such a strong PSU. My old Eurocase 350W PSU has 185W on 3.3V+5V.

EVGA 500W PSU has the following rating - 3.3V - 24A, 5V - 20A, 12V - 40A. Power output is only 120W on 3.3+5V and 480W on 12V. That is clearly a PSU for modern computers.
Evolve 500W power output is only 84W on 3.3+5V. My old Evolve 350W has power output 126W on 3.3+5V.

In your case it may be most economical to buy a used 500W PSU about the same spec as my Chill or my 350W Eurocase PSU. Those will work for sure and will cost 1/3-1/4 of new one. Just open and inspect it when buying it.

Cleaning and lubricating the fan will likely resolve the issue. You could also replace it with a new one.

While you're in there, just check the caps for any bulging. But it's likely it will be in perfect working order. I have a 27-year-old one that's still chugging along just fine.

SScorpio wrote on 2021-06-27, 21:43:

Cleaning and lubricating the fan will likely resolve the issue. You could also replace it with a new one.

From what I remember, it was that noisy even when it was new. I guess I could try to replace it, I've just never mess with PSU before.

AlexZ wrote on 2021-06-27, 21:22:

Your Athlon will draw power from the main 20 pin connector. I would recommend PSU that has strong 3.3V+5V rail, comparable to yo […]
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Your Athlon will draw power from the main 20 pin connector. I would recommend PSU that has strong 3.3V+5V rail, comparable to your old PSU. You won't be using the 4 pin 12V connector from your new PSU. If it comes with SATA connector you can use an adapter.

To put it into perspective my old Chill 510W PSU has the following rating - 3.3V - 33A, 5V - 45A, 12V - 25A. Power output is 330W on 3.3V+5V and 480W on 3.3V+5V+12V. Of course you don't need such a strong PSU. My old Eurocase 350W PSU has 185W on 3.3V+5V.

EVGA 500W PSU has the following rating - 3.3V - 24A, 5V - 20A, 12V - 40A. Power output is only 120W on 3.3+5V and 480W on 12V. That is clearly a PSU for modern computers.
Evolve 500W power output is only 84W on 3.3+5V. My old Evolve 350W has power output 126W on 3.3+5V.

In your case it may be most economical to buy a used 500W PSU about the same spec as my Chill or my 350W Eurocase PSU. Those will work for sure and will cost 1/3-1/4 of new one. Just open and inspect it when buying it.

I'll check what my current PSU is to compare it to a modern one. I've look at a few others and they all seem to be around 100-120W for the 3.3V+5V, guess I'll have to check for a used one, but doesn't like there's much on eBay at the moment. Thanks!

Your 500MHz K7 CPU won't draw more than 50W from the +5V rail. (Including losses from voltage conversion.) The rest of the motherboard and the RAM usually rely on the +3.3V rail and won't draw more than 20W combined.
Not knowing your PC's other components I can't recommend anything but I hope this puts things in perspective.

Also keep in mind that PSUs are often group regulated meaning some need a certain load balance on all rails or some rails will get out of balance (i.e. some modern units will output low voltages on +5V/+3.3V if there's high load on those rails but low load on +12V, others (fewer) will output higher voltages on +12V under the same conditions.)

Doornkaat wrote on 2021-06-28, 08:28:

Your 500MHz K7 CPU won't draw more than 50W from the +5V rail. (Including losses from voltage conversion.) The rest of the motherboard and the RAM usually rely on the +3.3V rail and won't draw more than 20W combined.
Not knowing your PC's other components I can't recommend anything but I hope this puts things in perspective.

I just check and it's in fact a 1 GHz Athlon, don't know why I tought it was 500 Mhz. It's one of the first Socket A Athlon I think, don't know if that helps. I've seen that it uses 54W, but that doesn't sound right if a 500MHz uses around 50W, unless the Socket A is just so much more efficient than the Slot A.

I also have a Geforce4 MX 440, a Sound Blaster Live Value, a CD Burner and a SATA HDD with a IDE to SATA adapter. I guess I should look at PSU that can deliver at least 150W on the 3.3V+5V, right?

Current requirements might depend on which motherboard you're using. I've got an Abit KA7 Slot A which (from memory) uses +5V as the input to the CPU voltage regulators, then uses the +12V to supply an on board 3.3V regulator, which is used for all the 3.3V on the board, and also for the input to the AGP regulator. So the PSU 3.3V isn't used at all.

ced_122 wrote on 2021-06-28, 19:40:

I just check and it's in fact a 1 GHz Athlon, don't know why I tought it was 500 Mhz. It's one of the first Socket A Athlon I think, don't know if that helps. I've seen that it uses 54W, but that doesn't sound right if a 500MHz uses around 50W, unless the Socket A is just so much more efficient than the Slot A.

The only 500MHz Athlon is the older Argon model. Its core is made on a larger process and the L2 cache consists of two external chips. It is a lot less energy efficient than the Thunderbird core. The numbers are plausible.

I also have a Geforce4 MX 440, a Sound Blaster Live Value, a CD Burner and a SATA HDD with a IDE to SATA adapter. I guess I should look at PSU that can deliver at least 150W on the 3.3V+5V, right?

150W +3.3V&+5V combined puts you on the very safe side with some overprovisioning. Athlon XP machines with high end Geforce 4 or FX cards would be fine with 30A@+5V.
I'd say a worst case power consumption of 100-120W on +3.3V&+5V combined is more realistic for your system, especially since your GPU has a pretty low power draw. You're probably looking at less than 50W on +12V.

snufkin wrote on 2021-06-28, 21:05:

Current requirements might depend on which motherboard you're using. I've got an Abit KA7 Slot A which (from memory) uses +5V as the input to the CPU voltage regulators, then uses the +12V to supply an on board 3.3V regulator, which is used for all the 3.3V on the board, and also for the input to the AGP regulator. So the PSU 3.3V isn't used at all.

Is that certain? Neither chipset nor RAM use +3.3V? While this may of course be possible I would be pretty surprised if a board was deaigned like that.

Doornkaat wrote on 2021-06-28, 21:12:

snufkin wrote on 2021-06-28, 21:05:

Current requirements might depend on which motherboard you're using. I've got an Abit KA7 Slot A which (from memory) uses +5V as the input to the CPU voltage regulators, then uses the +12V to supply an on board 3.3V regulator, which is used for all the 3.3V on the board, and also for the input to the AGP regulator. So the PSU 3.3V isn't used at all.

Is that certain? Neither chipset nor RAM use +3.3V? While this may of course be possible I would be pretty surprised if a board was deaigned like that.

That's my recollection. I was having problems with faults on some RAM and suspected a power supply issue, so tried to trace it. RAM had two possible 3.3V supplies that the motherboard could switch between via an 8 pin dual P/N FET. One was regulated from +5VSB, to be used in sleep mode, and the other from the on board 3.3V, powered by +12V. I did try lifting the 8 pin switch FET and connecting the RAM directly to the PSU 3.3V, but that didn't help. In the end the problem turned out to be heat build up toward the top of the sticks where there was no airflow. I'm pretty sure that there were no surface tracks visible from the PSU connector on the 3.3V pins, although they may attach to internal planes, but I never found anything that connected to PSU 3.3V.

If you want I might be able to double check that this weekend.