I can't take credit for the 70% rule because I read it somewhere, myself. However, I can add an opinion or two
It's OK to economize if you aren't doing anything unusual.
Most people can get by with a name brand 350 watt power supply, (well at least before FX6800. We'll see).
What's unusual?
- Overclocking
- Arrays of hard drives
- lots of fans
- high temperature situations. Remember PSU ratings are at 25 degrees C. If your case is running hotter than this then your max power is reduced.
- specific hardware situations
For example a P4 system derives power from the 12V rail. You need a PSU with a good +12V rating.
Athlon motherboards (32-bit Athlons) usually derive CPU power from the +5V rail. +12V power is less critical, or rather is utilized to a lesser degree. (It's still critical). You might choose a different PSU for an Athlon system than you would for a P4.
None of this means it's essential to upgrade the power supply. It just helps if you have an idea how your own components use power.
Pay more attention to the things that use a lot of power, like CPU, GPU, large numbers of PCI cards, large numbers of disk drives, overclocking.
LOL!
If only I would take my own advice. I've been pushing my PSU too far for a long time. I've had stability problems because of it.
<b>56K, slow and steady does not win the race on internet!</b>