Verdict: Silent, stable and incredibly efficient

FSP is one of the largest PSU manufacturers in the world and is the only company that was brave enough to send us a passively cooled PSU. We say brave because all the passive PSUs we've tested previously have blown up or caught fire.

While the Zen is rated at only 300W, it has a sensible modern design of two 12V rails comprising a 12V1 rail rated at 8A and a 12V2 rail rated at 14A. Both the 3.3V and 5V rails are rated at 20A. As this is a passively cooled PSU, it makes absolutely no noise, which was a real pleasure after being nearly deafened by the Cooler Master Real Power 550W. The Zen has connections for both 20- and 24-pin motherboards, and there are six Molex, one FDD and two S-ATA plugs.

It's only really possible to passively cool a PSU if it's very efficient, and the Zen sets new records for efficiency. While producing 298W, it drained just 349W from the mains - that's an efficiency of 85 per cent, well ahead of all the other 29 PSUs in this Labs test. The Zen also provides very stable voltages on each of its primary rails.

Despite only being rated at 300W, the Zen should still be capable of powering a PC with an Athlon 64 or Pentium M and a mid-range graphics card such as GeForce 6600 GT, thanks to its dual 12V rail design. And, because it's passively cooled, it's an ideal PSU for a media PC too.

• Cases - 21st November 2008
• Motherboards - 24th October 2008
• Gaming Headsets - 26th September 2008
• Dream PCs - 24th September 2008
• Headphones - 12th September 2008
• Media PC components - 22nd August 2008
• PSUs - 14th July 2008

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• Creative Sound Blaster X-Fi Titanium Fatal1ty Pro - Sound cards
• Multiwinia - Games
• Zotac GeForce GTX 260² - Graphics cards
• Sapphire Radeon HD 4850 X2 - Graphics cards
• Scan 3XS X58 Core i7 - Desktop PCs