for question 1)
according to the extreme power supply calculator "Electrolytic capacitor aging. When used heavily or over an extended period of time (1+ years) a power supply will slowly lose some of its initial wattage capacity. We recommend you add 10-20% if you plan to keep your PSU for more than 1 year, or 20-30% for 24/7 usage and 1+ years" .. thats quite a bit if u ask me. customers of mine dont plan on upgrading every year like i do.
Extreme power supply calculator, as its name might suggests, tends to overestimate a lot. I don't know where the author found the above statistics. It's likely he's exaggerating, similar to what he does in other parts.
I have been researching on this subject in these days. Take a look at the following chart:
http://www.low-esr.com/endurance.html-ssi
If your PSU uses decent capacitors, which should be common, rated at 3000 hours (at 105 degree C). Such a capacitor can work for 192,000 hours (at 45 degree C). It would mean nearly 22 years of 24/7 usage. So it seems they can last for a long time. I believe we can use a PSU for a long time (at least 5+ years) without losing much capacity. Adding 10% to account for the capacitor aging should be very safe.
AAnet uses actual wattage (in actual tests) to calculate the total wattage that our computer needs, together with a lot of useful information.
Here's my comparison.
AAnet:
http://web.aanet.com.au/SnooP/psucalc.php
Specs vs Actual Consumption
I tried to compare the value given in each component by each calculator. I found something interesting. Outervision is trying to be very conservative and will usually take the extreme/max values. It does what other simple PSU calculator does (trying to be way overestimate just to be safe).
Aanet is very special in that it tries to be as realistic as possible (while being safe not to underestimate). It uses the actual wattage from the test results to do the calculation. It breaks down the steps and does not give only one single answer. Instead of reading the recommendation only (which is a wrong way to do), you should read all parts in "Actual System Power Consumption"!!
Some comparisons:
Outervision = (OV)
Aanet = (AN)
Product ======================== OV ===== AN (Difference)
CPU:
AMD Athlon 64 X2 3800+ (Manchester) ==== 89 ===== 47 (-42W)
AMD Athlon 64 X2 4800+ (Toledo) ====== 110 ===== 70 (-40W)
Intel Core2Duo E6300 (Allendale) ======= 65 ===== 44 (-21W)
Intel Core2Quad Q9300 (Yorkfield) ===== 103 ===== 58 (-45W)
Intel Core2Extreme QX9650 (Yorkfield) == 130 ===== 85 (-45W)
[Note: Regarding the watt usage in AN, the default wattage used by AN is the peak wattage at heavy/full load from actual tests]
Graphic card:
ATI HD2600Pro ================== 25 ===== 22 (-3W)
ATI HD3650 ==================== 45 ===== 37 (-8W)
ATI HD4850 ==================== 99 ===== 99 ( -- )
ATI HD4870 =================== 144 ==== 124 (-20W)
nVidia 8600GT ================== 38 ===== 38 ( -- )
nVidia 9600GT ================== 54 ===== 51 (-3W)
[Note: Regarding the watt usage in AN, the default wattage used by AN is the peak usage. The actual value is adjusted a little to be closer to what the graphics card would be continuously drawing in gaming]
Hard disk drive (HDD):
SATA HDD: 24/HDD (OV)
Generic HDD: ~7.875/HDD [when gaming], ~11/HDD [for fileserver] (AN)
Others:
RAM DDR2 (800) ================ ~4.5 ==== ~1.5 ( -3.0W)
Floppy drive =================== ~4.6 ===== 0.0 # (-4.6W)
DVDRW Drive ================= ~26.8 ===== 0.0 * (-26.8W)
Blue-ray Drive ================= ~28.8 ===== N/A
PCI (average) ================= ~13.4 ==== ~2.0 (-12W)
USB device ==================== ~2.3 ==== ~0.5 " (- 2W)
Firewire ====================== ~7.2 ===== N/A
#: The author excludes the option of FDD because seriously they only use power when accessing the floppy drive, so unless your running crysis off your floppy drive it's not going to make a difference.
*: Only the 5V Amp is changed (+0.3A).
": Low-powered USB device consumes 0.5W, high-powered USB device consumes 2.5W.
Reference Power Consumption:
http://www.tomshardware.com/reviews/power-saving-guide,1611-4.html
http://www.behardware.com/art/imprimer/670/
Comments
Outervision is a conservative calculator. Expect to buy an overwatt PSU that you may not need. In addition it appears this site has partnership with various PSUs (ads!). I don't know if it's part of the reasons why it is considerably conservative.
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CPU: It simply takes the values from the manufacturers'. It's the safest but the manufacturer usually overstates their watt usage. For example Intel states 65W TDP across many Core2Duo products. In reality it is very normal that the actual wattage is a lot different from the quoted TDP value of the CPU
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Graphic card: It's ok. However the wattage when both cards run in SLI/F is inaccurate. It's wrong to simply multiply the wattage by twice. The actual wattage is more complicated, depending on the card, motherboard etc.
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HDD: 24W per SATA HDD looks crazy. I think hardly any HDD needs over 20W. As an example, WD Caviar SE series needs less than 10W while reading/writing according to the manufacturer specifications. Slightly less (~0.5W) when it is idle.
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Others: It goes too far when measuring the possible watt usage under "Others". They are way over-estimating. For example, there are few USB devices consuming 2.3W. Devices like USB keyboard, mouse, RAM stick etc. usually need less than 0.5W.
Aanet is an aggressive calculator. It wants to get as close to the max watt usage our system really needs, with some headroom on top for safety.
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CPU: It is much more realistic and accurate. The values are the peak values at 100% load taken from the actual tests.
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Graphic card: It's slightly better than Outervison's. However the wattage when both cards run in SLI/CF is also inaccurate. It's wrong to simply multiply the wattage by twice. The actual wattage is more complicated, depending on the card, motherboard etc.
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HDD: the values are taken from actual tests. The values are most realistic if your HDD is list. Otherwise you can select "generic hard disk" or any specific HDD close to yours. But then it is safer to add a few watt per HDD above its calculation, especially when your computer uses a lot of HDDs, acting as fileservers or having heavy hard disk activities. 10-15W would be a safe while realistic range of figures for 3.5" HDDs. It would be 3-5W for 2.5" HDDs.
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Others: It is being more realistic on the actual consumption of the components under "Others". It even takes RAM overclocking into account while Outervision lacks it. Although it can cover most typical or normal situations, it may get too aggressive in a few cases (eg non-typical systems which are heavy on PCI bus). Fortunately nearly all decent PSUs can accommodate your system with more than enough watt from 3.3V/5V rails, though the total watt required (in the worst scenario) will be slightly underestimated.