Well, in my experience a decent 300W PSU from back in the day had at least 30A on both the 3.3V and 5V lines. This is something you'll see very seldom in modern power supplies. Fortunately, Socket 7, Slot 1 and Socket 370 platforms use very little power, so you'll be fine with about 120W on those lines. The problems start when you want to fool around with 5V-heavy AMD setups (your Slot A and early Socket 462 boards). For them, you need some serious juice on those lines and it's almost impossible to find new power supplies that meet the specifications. You will *probably* be fine with a modern 650W-850W power supply that can supply 25A on both the 3.3V and 5V lines for a combined wattage of 150W, but even this is equivalent to a 250W power supply from back in the day. When it comes to later Socket 462 motherboards, you'll be fine with modern power supplies since they use the 4-pin CPU power connector you get on ATX V2.x spec power supplies. The same goes for Pentium IV boards.

This is a topic that has been discussed a lot of this forum and if you search around you'll find more info. Some people are of the view that it isn't really something you need to worry about much, and to an extent they're right. If you consider the fact that your CPU will never actually run at 100% most of the time.

Even Athlon / Athlon XP setups are usually ok with a quality PSU that has >= 20A on 5v. I have run K7 1000 and Athlon XP 2000+ on such PSUs.

Yeah, solid advice from swaaye there. Like I said, your processor will probably run at 100% load less than 1% of the time. It's also easy to forget that power supplies from that era were really low quality compared to the ones you get nowadays.

Edit: I was goofing around on a local site and I discovered the RaidMax RX-530SS. You can pick these up for $45 apiece. Why is this so interesting? Note the site below:

http://www.raidmax.com/rx-530ss.html

Apparently it can deliver 512W combined on the 3.3V, 5V and 12V lines. Although, if we consider the amperages we will see that it can deliver about 125W on the 5V line and 82.5W on the 3.3V line. The only problem is that they use Andyson as an OEM. From what I've read, they're not really known for making quality stuff.

I also think that StarTech makes new 5V-heavy 300W/400W power supplies, but they are very expensive and can go for up to $60.

Since you are talking about 486 systems (which take only a tiny bit of power), it will be perfectly okay.

A 486 CPU has a TDP of around 5W. That's 1A at 5V. Other components will take some but it still won't be much.

The most demanding processor powered from the 5V line is probably Athlon Thunderbird 1.4 GHz. I have measured 84W power consumption for that one (directly on the 5V line - 18,2A @ 4,6V). Athlon 1000 takes 53W, Pentium Pro 200/256 = 36W, Pentium Pro 200/1M = 48W, PIII Katmai 500 = 35W. So 20A @ 5V PSU should be be good enough for most systems of this era. My testbed is powered by 460W Delta PSU with only 21A at 5V and everything was running just fine - TB 1.4 included. The relatively big voltage drop was most likely caused by my measuring equipment, not the PSU itself.

It just occurred to me that the random reboots I got on my dual pentium 3 system were probably PSU related, rather than memory related, as I initially thought. That machine has a new EVGA 430W PSU, which is only 15A on the 5V. Two 700MHz Pentium 3's could draw upwards of 70W, or 14A.

I just found these on eBay: http://www.ebay.com/itm/400690844891 as someone mentioned StarTech. Seems like a good price.

It's a little bit better than what you had, but you'll probably end up with the same problem. I'd rather go for one of these http://www.ebay.com/itm/ENERMAX-353W-ATX-PSU- … =item3aa62127dc .

Couldn't find one of those Enermax's listed that would ship here. Looks like a solid PSU, though.

I'm hoping the StarTech will be better than you say. It says 28A on the 5V, vs the 15A on my modern PSU. Should be a significant improvement if StarTech specs are reliable. Startech also has a 450 model in that same series that is rated at 44A on 5V, but I couldn't find any of those.

Thermaltake still makes (or up until very recently still made) a ~400W model with ~30A on the 5V. They have an older variant that provides 40A too; not sure how common such a thing would be used. Mine has held-up well over the last decade fwiw (this PSU: http://www.newegg.com/product/product.aspx?It … N82E16817153006). For the older machines, StarTech actually has an AT power supply: http://www.startech.com/Computer-Parts/PSUs/A … ply~PS2POWER230

And looking at some of their ATX models, 30A is possible on a 300W variant:
http://www.startech.com/Computer-Parts/PSUs/A … ply~ATXPOWER300 (this one provides 30A)

As Evert said though - unless you're getting into later 5V-heavy AMD systems with a lot of 5V heavy accessories/peripherals, even a modern 15-20A/5V ATX PSU should be fine. A lot of machines from "back when" usually only had a ~100-200W PSU out of the box anyways, so you shouldn't have a problem with a "light" system like a P3 or PMMX on a modern PSU.

You can also get past the whole 5V problem with Socket A platforms by going for a VIA KT600 chipset motherboard. There are quite a few of them with ATX12V connectors for the CPU, this way you don't have the problem of having no juice on the 5V line. As far as I know, the KT600 is also very well supported on Windows 9x, unlike the nForce 2 chipset boards.

Some nForce2 boards have ATX12V as well. ATX12V seemed to arrive with Athlon with 2002 boards. But again 5v really isn't a big concern for non-SMP motherboards.

nForce2 also works fine with Win98. I've run it. Maybe I'm not aware of some quirks?

I don't have any personal experience with nForce 2 chipsets and Windows 9x, but there are numerous accounts of the drivers being unstable on Windows 9x. Not that Windows 9x is the most reliable environment to begin with. But, yes, nForce 2 boards have ATX12V connectors.

I've had good luck with Seasonic SS-300FS and GS supplies, these are available on eBay. They have 30A on +5V and 28A on +3.3V. I have a Tbird 1200/GeForce 3 system running on one without any issues.

Thanks for the tip!

This is beyond stupid, but you could use a Corsair AX1200i since it can supply 30A on both the 3.3V and 5V lines for a combined output of 180W. You'd be better off looking for a second hand unit than wasting your money like this.

I've found another good power supply for a 5V heavy setup

The Aerocool VP-1200:

As you can see, it can supply 170W on both the 3.3V and 5V lines. They are more expensive than buying one of the 250W/300W StarTech models, but if you want a modern quiet power supply, I'd say that this isn't a bad place to start.

Edit: Pardon me, while I interrupt myself. Here are the specs for the StarTech 250W and 300W ATX power supplies respectively:

250W

300W

It looks like the VP-1200 falls right in-between these two in terms of 3.3V and 5V current.

If you want to live a little more dangerously, you could buy an Aerocool VP-750. It can supply 24A on the 5V line and it can supply 150W on the 3.3V and 5V lines combined.

AllUrBaseRBelong2Us wrote:

It just occurred to me that the random reboots I got on my dual pentium 3 system were probably PSU related, rather than memory related, as I initially thought. That machine has a new EVGA 430W PSU, which is only 15A on the 5V. Two 700MHz Pentium 3's could draw upwards of 70W, or 14A ...

Problem with group-regulated modern PSUs is not only that the +5V rectifier is relatively undersized, but also that the whole PSU is designed for the heavier +12V loads and lighter +5V loads of modern systems.

When confronted with the opposite situation (lighter +12V and heavier +5V loads, like in a venerable Athlon XP system), in a typical unexpensive group-regulated PSU like the Corsair CX430 V2 the +5V voltage regulation gets FUBAR:

https://www.techpowerup.com/reviews/Corsair/CX430_V2/5.html

^ In the 'Crossload 1' test +5V drops below ATX spec. Ouch ouch. 😵

Higher quality (and more expensive) modern PSUs like the Seasonic S12G 450W (SSR-450RT), with DC-DC conversion and semi-synchronous rectification for the minor rails (as opposed to group-regulation) can handle the light +12V load / heavy +5V load scenario much better, without voltage sag in the 'Crossload 1' test:

http://www.techpowerup.com/reviews/Seasonic/SSR-450RT/5.html

But the +5V rail is still relatively weak at 20A tops.

Does anyone have any information on the build quality of StarTech power supplies?

I have reason to believe that they are based on the FSP-built units that AOpen used back in the day.