They would use very low power components beyond the P4.
Not really... it was the same standard components everyone else used. People tend to vastly overestimate the amount of power required by computers. Part of that's probably attributable to the fact that the average $20 "500W" power supply that most people buy is usually only good for 200W in reality.
I have a Dell Optiplex here with one of those 90W PSUs. It has a 600mhz Katmai in it, the single most power-hungry PIII made, and the entire system draws 35W from the wall at idle, and around 80w under full load. I doubt the PSU is super efficient, either, so the actual loaded DC draw is probably more like 60W.
I don't know the power consumption of a Voodoo2, but it's unlikely to be more than 10-15W per card considering that the things can get away without even a heatsink. A Rage Fury MAXX can't draw more than about 25W, simply because that's all a standard AGP slot can provide without the extra AGP-Pro power connector or an external molex. While there may be some draw on the 12V rail, it wouldn't be more than a couple amps at most... the bulk of the draw is going to be on the 5V and 3.3V lines.
Considering that Seasonics are generally pretty honestly rated, that 200W PSU should be plenty as long as it's in good shape (i.e., caps haven't degraded), and you're not running a bunch of hard drives or anything.