I really dislike the *censored* that started this more Amps on 12v rail = better argument... Now everyone and his kid sister will label their PSUs with high Amp rating...
No... seriously, don't go that way. Here's how I would choose a PSU:
- Brand... is as important as your life. A good brand PSU can withstand years of beating from beastly hardwares. Choose your brand wisely. Thermaltake, Antec, OCZ, PC Power and Cooling, etc... are some of the ones I would trust. The rest, I would just push down the drain. But it's all about your experience with them, really. If you don't have any experience, pick one and find out for yourself. Sounds risky, but it's true... You grow on failures.
- Never ever EVER buy a top-tier model. Actually, get the almost cheapest model you can find from the brand. This is where you look at the price tag and go: ohh, let's get it! No, seriously... The top-tier parts can sometimes be cheaper than even the low-tier parts. Why the contradiction? Well, because top-tier parts sell well to enthusiasts. Cheap parts are only purchased by either cheap people, or system builders looking to build something that just works, and seriously, people who buy pre-made computers are even less likely to look at these... so sale from that section won't amount to much if at all. Meanwhile, the top-tier models are usually very appealing to the enthusiast market, and these would either be in competitions, or for gaming systems (a.k.a. they don't last long), which is to say, they can generate a lot of revenue with these if they price them right. Ever wondered why a 700W PSU that went for $150 last year is now only $40 refurbished in a corner of the internet? That's the reason...
- Wattage rating... Now this is a little bit trickier. You can calculate wattage by multiplying the V ratings with their respective Amp rating then add them all up. Then the sum would be the correct wattage rating, not the number printed on the label. So, say... The PSU above would have this kind of wattage:
3.3 * 36 + 5 * 38 + 12 * 40 = 788.8W
So why is it rated at 750W? Because there is inefficiency in the PSU working. The power it draws aside, the power output it can do is at most up to the calculated value, but it can flunctuate anywhere in between and even lower. If it's not rated for 80plus efficiency (power draw rating), then it might actually not reach its potential max output. Why? Because it can only draw so much from your socket. If it can't draw enough power to sustain the load, then I'd say you are looking at realistically... around 70% the max output, which is 550W in this case. So... do the math, weigh the options, look for the labels, then nail it. And by the way, the algorithm above would only take into account 3.3v, 5v and 12v, the rest is just disposable garbage from my experience.
- Amp rating... Now this is where the lie begins. If you see the PSU has multiple 12v rails, it'll say something like 12v1 16A, 12v2 16A, 12v3 16A. Does that mean the 12v rail can only output 16A? Heck no... That means the 12v rail, as a whole, can output 48A. Since there is no multi-rail 12v, it's just a single 12v rail split into 3 in this case. But what if you see a manufacturer write 12v1 32A, 12v2 32A? I'd stare at that with my jaw dropped to the floor. A PSU that is so powerful, it can push 768W through 12v? Kinky... Ahem, anyway, you shouldn't worry about the 12v ampage as much as people would like you to. Why? Because... it's mostly just for your GPU that you'd need that much watt for. But how do you know how much a GPU draws? Well, that's the tricky part. Ever seen those power consumption tests in benchmarks and reviews? Yeah, those... You take that power consumption figure (of the GPU alone, by the way), then multiply that by 80%, since power draw is not the same as power requirement, and then you'll have the right wattage necessary for a GPU to operate. So, for instance, the GTX 260 would use a max of 230W in most reviews. You get 184W as the figure after multiplying by 80%. Now divide it by 12... and you get... 15.3! yep, folks, the GTX 260 doesn't really need more than that on a 12v rail to survive through hell and back. Even if you overclock the heck out of that mofo, I'd say you need at most a 20A rail stable... Add 4A or so tolerance to that number (for other peripherals, fans and stuffs) and you'll have your correct rail rating, which is around 18A to 19A, realistically, give it 20A or 22A for more breathing room. So, sincerely, unless you plan on going extreme... 30A or more is just too overkill for a budget build... and if it's a no-name brand, even I would start sweating...
So, really, I don't think you'd need that beast of a PSU for any reason at all. You just need one that is stable... and works well. So choose your brand wisely, weigh your budget, think about the configuration you are aiming for, then calculate a whole lot. Leave breathing room, but don't overdo it.
And Schumi, this is one of the reasons why I can build PCs for so much cheaper than the other folks.
If you can take $50 off the PSU, that means you already can push for another grade of GPU. It matters.
