Ask Dan: Power-supply puzzlement

Date: 4 September 2007
Last modified 03-Dec-2011.


I have two computers which I have just purchased new 512Mb video cards for (one HIS ATI Radeon X1650 PRO ICEQ 512Mb AGP, and one Inno3D Nvidia 7600GS 512Mb AGP).

The ATI card is in the older computer that has an MSI MS-6330 LE3 motherboard and a 250W PSU. I am having trouble with the ATI card as it keeps on crashing/freezing the computer mid application/game. Is it because it does not have enough power? If so, what PSU would be compatible with the MS-6330 LE3 board, so that I know which one to buy?

I am not having any trouble at the moment with the Nvidia card, as my newer PC has a 300W PSU (peak rated 350W). Do you recommend upgrading the PSU on this one? If so, what PSU would be compatible with the board? (Gigabyte 8S661FXMP-RZ).


There's some disagreement about how much power the Radeon X1650 Pro draws.

Here and here you can see reviewers saying that it's good for almost 160 watts when working hard. That would certainly more than justify the big two-slot cooler that many X1650s have, but it sounds way too high to me. It would definitely be far too much for the passive cooler on this card to handle.

HIS AGP Radeon X1600 card

It's an open secret that the X1650 Pro is just a marketing creation. Technically, it's precisely the same as the older, more expensive X1600 Pro, except the X1650 has core and memory clocks of 600 and 700MHz respectively, versus 590 and 690MHz for the X1600.

If you think that sounds like no perceptible difference at all, you're right. And since the X1600 Pro was about a fifty-watt card at the absolute most, the X1650 Pro's sub-2% clock speed bump means it's a fifty-watt card, too.

To use a technical term: 160 watts, my arse.

That said, a 250-watt PSU is likely to be inadequate for any modern gaming PC, even if it's still rockin' a retro AGP motherboard. It's eminently possible that adding the new graphics card pushed that PC over the edge, especially when you consider the fact that PSUs do not improve with age.

AMD recommend at least a 350-watt PSU to run a "fully loaded" computer with an X1650 Pro in it. Other video card companies recommend different PSU figures, often a bit higher than the ATI number.

The higher estimates are usually to compensate for power-supply-manufacturer fake watts.

PSU-maker fake watts aren't nearly as bad as cheap-stereo-system fake watts, but they're still significantly inflated. For home users, though, the best value proposition is to recognise that cheap and cheerful PSUs often have ratings way above their real power delivery capabilities, and just buy a "650W" or something PSU to do a job like this.

The very cheapest high-rated PSUs, mind you, are complete junk. It's actually possible to find "ranges" of PSUs that have different ratings and different prices, but are all exactly the same inside. Sometimes they come with sheets of rating stickers which the retailers can apply as needed. That certainly makes inventory management easier.

The yum cha brands sold by reputable stores like Aus PC Market, however, are generally fine for home and small office purposes. Aus PC Market here in Australia, for instance, will sell you a "650W" GTR-branded PSU for a lousy $AU165 including delivery (Australian shoppers can click here to order it!). That'll run your X1650 PC just fine, even though I'd be surprised if its real rating was above 400 watts.

Your MSI MS-6330 LE3 motherboard doesn't have any odd power requirements - it's not a server board that needs one of the unusual auxiliary power plugs, for instance - so you shouldn't have to worry about getting it to work with any current-model mainstream PSU.

Your old motherboard will have the old 20-pin main ATX power socket on it, but new-style 24-pin plugs still work with the old connectors; worst case scenario, you just plug them in with the extra four pins hanging over the edge. The plug and socket are keyed to make it impossible to line them up wrongly (well not without using a hammer, anyway), but it is possible for the unused part of the new-style plug to hit components next to the socket. Fortunately, most PSUs - including, I think, the cheap GTR one - have a "20+4 pin" plug, in which the extra four pins are a separate sub-plug that you can detach if it gets in the way.

The days when cheap and cheerful PSUs came with enough connectors for about half of the components in an average PC are also, thankfully, gone; on top of the 20+4 pin ATX plug, the cheap GTR give you seven "Molex" drive power plugs, a generous two floppy-drive power plugs (a lot of high end PSUs these days only have one), four SATA drive power connectors, one PCIe video card power plug, and another split "4/8 pin" auxiliary power plug, accommodating both varieties of "ATX12V" extra motherboard power connector (neither of which exists on your old AGP board).

The GeForce 7600 GS in your other computer draws a bit less power than the X1650 Pro. It might just make it to 30 watts if you pushed it really hard, but that's about the limit. And since that computer's got a beefier PSU, it's not surprising that it's working fine with the new video card.

Usual PSU recommendations for stacked 7600 GS systems are up around 350 watts, but it's perfectly possible for an honestly-specified 300W PSU to be fine if there's not too much other load from the system. PNY only say you need 300 watts for their AGP 7600 GS.

So if that computer works, don't worry about it.

I always recommend people keep a spare PSU on the shelf, because it's not very expensive and makes it easy for you to do a quick swap if Very Weird Symptoms arise in a PC. But there's no need to rush out and buy one.


Does this 650 watt Antec power supply have 4 pin connections that I can use for my IDE drives?

I am asking because I want to upgrade my PSU, and don't want to buy something that I will have to buy SATA hard drives for


The 650W Antec Trio PSU...

Antec Trio PSU

...has six standard "Molex" drive power plugs, plus a couple of the "fan only" variants that only have +12V and one earth connected (and which, in the case of the Trio, are connected to the same thermal speed control as the PSU's own fan).

Here's the product page for the 650 watt Trio, and here's its connector list. This is the page for the Trios in general.

Note that Antec's line about three separate 12V outputs "allowing you to distribute your power more evenly" is marketing bulldust. As I mention in my 2006 review of a couple of Tagan PSUs, dual 12V rails are indeed part of the ATX version 2 specification, but they don't necessarily provide any end-user benefit.

Transient super-high current draw from one component can cause the 12V output that component's running from to temporarily dip well below spec, and it's theoretically beneficial to split the computer up into two or more zones, to limit the number of other components that such a glitch will affect. The abovementioned 1200W Thermaltake unit has no fewer than four 12V outputs, two rated at 20 amps and two at 36A (...and yes, that adds up to 1344 watts in total before you even take the other rails of this "1200W" PSU into account, which tells you that you definitely can't fully load even all of the 12V rails at once).

It's perfectly possible for a PSU manufacturer to just ignore ATX v2, though, and run all of the PSU's 12V outputs in parallel from one super-beefy regulator circuit. In practice, that's likely to work just as well, as long as the one monster circuit isn't very optimistically specified, as they often are in simpler PSUs.

The only real problem with the one-12V-rail idea for most purposes is that a PSU that can deliver several hundred watts through one wire will happily do so if that wire gets shorted to ground. A single-12V-rail version of a "1200W" PSU might be able to deliver a whole kilowatt at 12V, which could cause something quite impressive to happen if you slammed the case closed on a drive power cable.


Is this 1.2 kilowatt (!) Thermaltake PSU for me?

Thermaltake Toughpower PSU

My rig is currently
A Socket AM2 Athlon 64 X2 5000+
Gigabyte GA-M59SLI-S5 motherboard
Gainward GeForce 8800 GTX
Areca RAID card <-- where things start getting silly
Eight Seagate Barracuda 7200.10 SATA hard drives
850W Silverstone Silverstone Silverstone Zeus PSU (cooling isn't an issue)

I added an extra (Leadtek) 8800 GTX card to this PC, and it now has problems POSTing (raid card just keeps beeping at me) and when it gets into Windows, it locks up very quickly.

Will this fix the problem, so to speak?


I'm not sure.

The GeForce 8800 GTX really is a 160-watt graphics card, but only when it's working hard. Your new card isn't working hard when you're just booting the computer and looking at the Windows desktop.

Every flavour of 8800 is still something of a pig even in 2D mode, though. An 8800 GTX can somehow consume seventy watts when it's doing nothing in particular, versus maybe 30 watts for cards a couple of rungs lower on the performance ladder.

So it's possible that the new card really has pushed your computer over the edge into flaky-power territory. But I wouldn't bet my life on that. The new card may be defective, or you may have static-zapped it when you installed it; if you take the old 8800 out and using the new one by itself, and still have problems, then the new one is probably sick.

Or it may be a quirk of your motherboard. Update to the latest BIOS version and see if that helps.

Or there may be some weird compatibility issue between the Gainward 8800 and the Leadtek one.

As I've mentioned before, there is not officially supposed to be a problem, any more, with using identical models of Nvidia graphics card from different manufacturers in SLI mode. That used to be a recipe for trouble, but Nvidia's drivers fixed it as of version 80.

All things are, however, possible, in this best of all possible worlds. Perhaps your two graphics cards just don't like each other.

Or, yes, it could be a PSU problem.

Your Silverstone PSU is, if this review's to be believed, a genuine 850 watt unit. So it ought not to have any trouble powering even an over-the-top computer like yours, unless Silverstone did something daft like connect all of the PCIe power connectors to one rail, or something.

(It's quite easy to hang a multimeter off a drive power connector while the system boots to see if there's a horrible sag, by the way. It's possible that all of your hard drives spinning up at once may now be overloading one of the PSU's outputs, and causing the RAID-card-beeping problem; your RAID card may have a staggered-spinup option that'll fix that. This also doesn't explain the quick Windows hang, unless something bizarre's happening like non-hotswap drives coming online after Windows has started.)

The Thermaltake Toughpower PSU you're considering unit is expensive, but seems to be surprisingly good value, if you actually have some use for most of its outrageous output capacity.

The Toughpowers are made for Thermaltake by Channel Well Technology, which is not one of the crowd of PSU "manufacturers" which are really just (frequently-changed...) names for a rather smaller group of cut-rate Chinese factories. Apparently you really can get 1200 watts - and a little more! - out of that Thermaltake.

(That suggests that the current top of the Toughpower range, the one point five kilowatt model, is also honestly rated.)

Realistically, of course, it's virtually impossible to get anything that uses an ATX-type PSU to consume 1.2 kilowatts, let alone 1.5.

Thermaltake put "Quad GPU Ready" on the 1.2kW Toughpower's box, and they're not lying, but there's not a lot of point buying a power supply today for the theoretical 600-watt showpiece graphics systems of tomorrow. The only way to actually get four SLI or Crossfire graphics adapters in a normal PC so far is by using a couple of Nvidia's strange 7900/7950 GX2 cards, each of which has two graphics chips on it. But even a pair of GX2s will lose on most benchmarks to a single GeForce 8800 GTX.

(A car cigarette lighter is only about a hundred-watt item, in case you're wondering...)

For this reason, the usual PSU recommendation for SLI 8800 GTXes is "500 watts plus", which you've already got. If you do something that absolutely wrings the neck of your current computer, you'll probably be able to get it to draw about 650 watts all told. Unless there's something wrong with your Silverstone PSU, which is possible but not high on the probability list, changing PSU won't do anything.

You're probably not actually ever going to be flogging all eight drives while you redline the CPU and both graphics cards, so a more realistic maximum sustained draw for your dual-8800 PC is likely to be more like 500 watts. It's a good idea to keep a PC's PSU running at well below its maximum (honest) output, but there's no need to go nuts.

I often recommend people try a new PSU early on in their troubleshooting, but not in this case. The high-end Toughpowers are pretty awesome pieces of gear, but I'm not at all sure that one of them will help you, and they're not cheap.

Still, they're good value. If you don't get anywhere with my other suggestions, it could be because your Silverstone PSU isn't healthy. And I doubt the 1.2kW Toughpower will do anything for you that the 850 watt one won't.

Aus PC Market stock the 600, 750 and 850 watt Toughpowers as well as the 1200. The 850 should be more than enough to run even your computer, and it's only $AU308 delivered, versus $AU489.50 for the 1200W.

If it were me, I'd probably end up dropping the extra dollars on the 1.2kW model anyway, just to be super extra double sure, and accommodate any future expansion plans involving arc welding or running banks of rally-car lights.

(Australian shoppers who'd like to buy the 1200W Thermaltake Toughpower PSU from Aus PC Market can do so here. More sensible people who'd prefer the 850 watt model can order it here.)