Several PSU-related questions

[jaffa]

I am about to buy a new psu but need to get some questions answered first.

I have heard that sometimes a 350W psu may be better and more reliable than a 450W psu. During which circumstances is that true?

What is the function of the Amp (why is higher Amp better)?

I have also heard that it is important to have high Amp on the 12V. Why is it so important for the 12V to have high Amp and not that important for the 3.3 or 5V?

Which is the minimum amount of Amp on the 12V I should have if I have a demanding cpu and a powerful video adapter?

What should the Amp on the 3.3V and 5V be at minimum.

 

[Zepper]

Most PSU makers know that the great majority of systems actually use less than 300 Watts. So if a PSU can provide those 300 Watts well then games can be played with the numbers above that. There are PEAK watts, Continuous watts, both of those with all rails loaded to X%, etc. etc.
. Newer systems power the CPU, high-end video cards off the 12V rail(s), fancy lighting or water cooling, (as well as drive motors and other things that were always 12V powered) that is why 12V Amps (think of volts as similar to watter pressure in a hose - think of amps as the flow volume thru the hose) are more important now.
. If your mobo lacks the P4-12V connector (or other auxiliary sources of 12V power for the CPU) and/or a high end vid card, then your PSU should be heavier on the 5V rail.

. A solid 20 Amps or higher should be fine for even high end stuff. Maybe a bit more for high end vid +SLI. Look at the Seasonic S12-330 for a good example of PSU design for the newer systems (and the little 300W PSU that's in the Chenming 118 cube case).

..bh.