I noted no fluctuation at all in the output during the idle state, and only a variance of .01v in the +3.3v and +5v rails while under load. I believe this is the most stable and unwavering output I have ever seen out of any power supply I've ever tested, and at voltages that are much closer to their rated levels too.
Thermaltake has not disappointed with its latest Toughpower QFan series of power supplies. The QFan 650 is a solid, high-quality supply that I feel would have no problem putting other higher-rated but lower-quality units to shame. The UL indicated manufacturer of this device is Channelwell, a company well known for producing very high-grade power supplies for a variety of resellers such as Antec and XClio as well as Thermaltake. One look at the specification and feature list should tell you that this is one power supply that takes no prisoners.
In addition to its extremely capable performance, the QFan series marks the latest step in Thermaltake's development towards producing a completely silent power supply. With the patented fan design and rubber vibration dampening sleeve, chances are you will never hear anything above a whisper. I could not hear it running even with my ear positioned at the rear of the case. I literally had to place my hand behind the exhaust vent in order to tell that the fan was indeed working. With the hardware in my test rig, there was no change in thermal or noise output even when running under load. It's certainly going to take a lot more than a dual-core processor, single video card system to put a strain on this power supply.
List cost on the Toughpower QFan 650 is around $175, with the 500 version marked about $50 less. Street prices should lower these figures 10-15%, but this is still on the high side of the scale when compared to other power supplies with similar specs. Not many brands offer the 80-Plus energy efficient certification however, and Thermaltake claims it will handle a 750w peak load for up to 60 seconds, so the 650 model number may be deceptively underrated. Either way I feel confident in stating that you will not be disappointed in this power supply.
OCIA.net has awarded the Thermaltake Toughpower QFan 650 our Seal of Approval.