Most computer builders in the world think I'm nuts for endorsing the use of 330 watt power supplies for a high-end performance computer. Conventional "wisdom" says that anything under 500 watts is inadequate for an enthusiast PC. "My power supply is bigger than your power supply" seems to be a typical mindset for many people but I've always had just the opposite desire to say that "my supply is smaller than yours and it works great". So when I started building mainstream dual-core computers with 220 watt 80 Plus power supplies, people were shocked that I would even consider such a small power supply. But since I was able to build a 50W peak power dual-core computer, why not use an even smaller power supply in the sub-100 watt range?
Pictured above is the open frame fanless AC input open frame 55 watt FSP055-50LM power supply from Sparkle Power Inc with an MSRP of $39. Typically when power supplies are this small, people often use DC input power supplies with an external AC brick. Not so with this model as it's an all in one with the standard AC power connector you get on a normal ATX PC power supply. It's so small that it doesn't even bother with a fan or metal casing; you have to a system-level fan yourself and provide the bracing and shielding in your computer chassis. The really nice thing about this solution is that the entire power supply including the AC conversion part is not much bigger than a DC power supply but you don't need an external brick.
Using this 55W power supply, I took a dual-core Intel E2140 along with the bundled ECS945-GM motherboard I bought for $90 and built a computer with it using default clock speed and voltages. Unfortunately since it was missing a 4-pin power connector for the motherboard, I had to hot-wire a 4-pin CPU power connector from an older power supply to this unit to make it work. That means 2 12-volt yellow cables and 2 black ground cables had to be soldered in to place and taped up. Since these cables are safe for 10 amps each which translates to 120 watts per cable, I'm not even close to overloading the cables.
Once the computer came up, the power consumption at the plug peak out at 70W which means the output power is around 52W at 75% efficiency which is 3W under the peak output of the power supply. That is cutting it a bit close but it shows the extreme worst-case of what this PSU can handle.
In reality, the 55W PSU isn't practical for a mainstream dual-core computer although it would be more than powerful enough for an Intel D201GLY with Celeron 115, D201GLY2 motherboard with Celeron 120, or the Via low-power ITX platforms. The upcoming Intel Centrino Atom platform with the Atom-Diamondville CPU peaks at around 4W TDP so they're even easier to power.
The bottom line is that this is a nice little power supply for small embedded solutions but you'll want to stick with the bigger 80 Plus closed-frame models like the Sparkle SPI220LE 220W or the SPI270LE 270W if you're building a mainstream PC. Note that the SPI models are 1U power supplies so you'll either need a very custom case or one that uses 1.75" thin power supplies.