On multi-railsThe Corsair HX series is not true multi-rail... except the HX1000. That is based on the same CWT platform as the Thermaltake Toughpower 1500W, and
has 2 separate PFC circuits. Personally I'm not too concerned about multi-rail capability, and it's not a deciding factor for my PSU purchases. They don't actually help to stabilise voltages anyway, unless both rails are on separate filters (rather rare). The main reason for multi-rail systems is supposedly for safety, to
avoid having >20A voltages on a single user-accessible cable.Preferred PSUsI tend to go for Seasonic-OEM units for <700W PSUs. That means mainly Corsair and Seasonic units. Seasonic's S12II series are a well-known budget option, their M12II are well-reputed mid-end units, and their X-series is one of the rare few fully modular, 80Plus Gold-rated PSUs. The Corsair VX/HX series have a similar reputation (the higher-wattage HX and TX units are CWT OEM PSUs though, not Seasonic.)
On modular cablesModular cabling is nice, but it adds extra cost to the PSU. If neat cable management and the idea of not having to discreetly tuck away unused cables is important enough to you to justify the price premium, go for it. Not all modular PSUs are equal though, some are only partially modular, i.e. you get 24-pin mobo, 4-pin ATX12v/8-pin EPS12V, and maybe some PCIe cables from the PSU, while the rest of the cables are modular.
On fansWhatever the fan used, all you need to look out for is whether it is quiet enough for you (if noise matters in your selection criteria), and provides enough cooling for the PSU. For that you'll have to check PSU reviews. Naturally, 120mm fans tend to be quieter and pull more air than 80mm fans, though that doesn't necessarily mean there aren't any quiet or effective 80mm fans.
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PSU wattage ratings (and why they matter less than most people think)Here I might also venture that the wattage rating on a PSU is usually the least important consideration (assuming you're not just looking for a PSU that does the job cheaply enough, and are looking for a PSU that best suits your needs). There is no standard wattage rating method among manufacturers, and you'll often find both PSUs that can easily provide above their wattage rating, as well as PSUs that will crap themselves below their rated wattage. Manufacturer rating serves as a quick guide for filtering your PSU choices (it's a bad idea to use a PSU rated lower than your peak system power draw anyway...), but other than that it simply isn't very useful.
This forum post summarises generically the various ways that less reputed PSU brands use to give their PSUs higher wattage ratings than they're actually capable of.
As an example, many generic or cheaper PSUs will have small-print stating that the rated power is peak power wattage and should not be sustained for more than 30 seconds (or thereabouts), or at temperatures above 50 degrees Celsius (which a heavily-loaded PSU can often exceed). On the other hand, there are also high-end units that are rated much lower than they can actually push, e.g. the
Corsair HX1000. This is done for various reasons, e.g. for 80Plus certification. Since that certification requires >80% efficiency at 20%, 50% and 100% loads, manufacturers may rate the PSUs lower to ensure that at 100% of the rated load, efficiency still stays >80%. (You really shouldn't be buying non-80Plus rated PSUs for a good build, anyway.)
Rough PSU checklistFor most intents and purposes, you really just need to ensure that:
1) The PSU isn't too inefficient at typical power loads. >80-85% is good enough for most people, go higher than that if you're an efficiency freak, or if (like me) you like spending more money on performance factors that won't matter to most people.
2) The PSU can comfortably handle your system's peak power loads for lengthy periods of time. You never know when you might want to try your hand at encoding or rendering, and the last thing you want is a PSU that starts (figuratively) sweating and panting at such loads. Note that this figurative effort has nothing to do with the rated wattage; at the very least, you want to ensure that the PSU doesn't run too hot (usually also indicating low efficiency or inadequate cooling) at such loads, which the manufacturer's wattage rating does not guarantee.
3) The PSU actually meets your needs. This bundles various other factors, some of which have already been mentioned above:
a) Ensure the cables are the right length (not too long if using an SFF case, and not too short if using a full tower case).
b) Check that the PSU fits your computer case (important if you're using a
SFF case).
c) Has the connectors you need. Especially check for ATX12V/EPS12V connectors; cheaper motherboards tend to have the ATX12V connector housing, while high-end motherboards have EPS12V. Not all PSUs are ATX12V-compatible, if you're pairing a high-wattage PSU with a cheaper motherboard, make sure it is ATX12V-compatible. Vice-versa if pairing a low-wattage PSU with a high-end motherboard (check EPS12V compatibility).
d) Has a cooling airflow path that is compatible with your case flow of choice. Most PSUs are now designed to pull air in front the side fan, and push it out the back (where the main power connector is plugged), but some older units still in stock (especially PC Power and Cooling units) pull air from the front (where the cables come out from) instead, or perhaps even use a back-to-front airflow pattern (quite rare though).
This is probably a non-consideration if you're buying a brand new PSU.This is a good guide for those looking for a quick list of recommended PSUs, and PSUs to avoid. You are still reminded to do your own reading though, and not to take everything at face value.
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On Fermi's reported power drawWait 10 more days and reviews of it will be out. Check the actual power draw for it then. If you read the
relevant forum thread, the 42A current requirement is for the whole system, not the GPU alone. That shouldn't be too difficult for most good >600W units to achieve (would you trust an expensive Fermi card with a cheap PSU, anyway?).
@vuzedome: What do you want to know about kilowatt units? I have a Corsair HX1000W and Silverstone OP1000-E (don't ask... let's just say my build plans changed drastically), and have used both for some time, although I've never actually loaded them anywhere near their rated limits. With regards to manufacturer-provided cables, PSU size and user experience I can maybe help to answer some questions, although keep in mind that my system power draw is probably less than 200W in typical usage scenarios. I am slowly working towards getting a Seasonic X650 as a replacement, but in the meantime this is all I have :x
