Antec TruePower 750W or Corsair 750W?

[sammorris]

PSU calculators like that are very over-zealous. When I had a Q6600 and a single 4870X2, I ran it with a Corsair HX 520W with no issues, my total DC power draw worked out about 400W, plenty of breathing room. Configuring that setup in outervision puts me at 530W.

Likewise, with my current system as it is, I run an 850W Zalman with no issue, and full load doesn't exceed 700W DC outside a stress test. The calculator puts me at 750W.
I have not allowed for capacitor aging in this tests, don't bother calculating as you've no idea what it will be. Just give yourself a requisite 20-30% extra space on top of your required wattage instead. In this instance, with two GTX275s, a 750W PSU will be about right.

[scaryjim]

Don't trust online PSU calculators - they're rarely even approaching accurate. There was a thread on here a week or so ago where someone used one: a number of regulars then used the same calculator to test their rigs and for most of them it recommended a PSU >100W above the PSU they were *actually using*.

If you're unsure, most Hexus reviews (certainly processor reviews) have a power draw reading at the end. Have a look at some of the i7 and graphics card reviews, have a careful look at the "system setup" page to see what components are included, then check the power draws. The test systems very rarely manage to pull more than 300W at full load!

[sammorris]

Also remember that such tests usually state load at the wall. Modern PSUs tend to be 80-90% efficient. Consequently, the amount of power the system in the test is actually drawing from the PSU is 80-90% of the value stated. For instance, TheTechReport's test uses an i7 965 Extreme, and when this was used with a GTX260, the total draw from the wall was 343W, so realistically you're looking at somewhere between 270 and 305W DC draw. Notably, two GTX285s in SLI with the same system drew 529W from the wall, so DC load is around 420-470W. Since the GTX275 used 11W more than the GTX285 (It's not a very power efficient card, but it is certainly better value than the 285), two GTX275s in SLI with an i7 965 we're looking at no more than 440-490W. Add a few hard disks, some cold cathode lights, hefty fans and more than the usual amount of RAM, perhaps we could nudge 550, but it'd be hard to do so.

[scaryjim]

Modern PSUs tend to be 80-90% efficient. Consequently, the amount of power the system in the test is actually drawing from the PSU is 80-90% of the value stated.

This is a good point: even more so for the Hexus tests because the high-end systems tend to get hooked up to a 1000W PSU! PSUs tend to be less efficient at low power draw than high, so in fact the draw of the system from the PSU is likely to be somewhat less than 80% of the measured figure in the hexus tests, where the PSU is being run at <30% of its rated value...

[sammorris]

Very true, efficiency slopes off much more at low power usage than it does at high. However, this tends to be more a fixed value than a percentage of total output. The ZM1000-HP is able to maintain 80&#37; efficiency down to about 70W load, 85% from about 120W all the way up to about 700W.

[cragside]

I thought the 823W was overkill - glad you thought so too!
but I'm happy with 750W anyway as it's still (just) in my budget of £100.

I'm getting the impression that Corsair makes the better PSU, unless perhaps it was up against one of Antec's signature series, which it isn't.