Ok, here is how power supply ratings work.
The wattage rating is the MAXIMUM wattage that can be drawn thru the power supply.
This DOES NOT mean that that is how much WILL be drawn.
Besides, I've only got like a 200 watt power supply on my G3, my athlon has a 300 watt.
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G3 400, 384, 12 + 75 GB
PM 8500 - 150, 176, 4.3 GB
PM 7100 - 66, 32, 700 MB
PM 6100 - 66, 40, 1 GB
And the lowest of all:
Athlon Thunderbird 954MHz, 128, 8GB