The +3.3v and +5v rails look great and are extremely stable, even when stress tested. In fact, the +5v line never moved. The +3.3v only dropped .01 under load which is very good. The +12v I thought was a little high to begin with, and it did come down under load, however it wavered from 12.25 to 12.29 which is a bit more fluctuation than I like to see.
I was impressed with the BFG Tech LS-550 power supply. For a standard-sized ATX with a smallish 550W rating it's got a nice heft to it. While weight certainly isn't the sole factor in how well a power supply will perform, it can be a good indication of the quality of the components. And the large 135mm cooling fan, open honeycomb vented back and mesh wrapped cables are not typical fare for a unit of this size. It's hard to believe that 550W is considered "small" by today's standards, when you commonly see 700W, 800W or even 1000W+ power supplies in use. But as tests have shown, a single video card system, even one with a quad core processor, would be hard pressed to require more power than something like the LS-550 can provide.
The mis-matched power ratings are a bit confusing. I thought it strange that BFG would have one set of numbers posted on their website and another on the power supply itself. But I suppose specs can change between the time a product line is developed and marketed to when it actually sees production, and by all appearances they have changed for the better. While 20A per +12v line is pretty incredible for a 550W power supply, we'll take BFG's word on it that the PSU will handle it. The only other hiccup I saw was a slightly overvolted +12v rail, and a small amount of fluctuation under load. Neither was anything to become overly concerned about, I would just be careful about putting too much of a load on the +12v line, such as running high end dual GPU configurations.
The BFG Tech LS-550 can be found online for just under $100. While I feel the power supply is definitely of high enough quality to demand such a price, given the relatively low power rating, this unfortunately puts it in a range where there is some pretty stiff competition. With some other manufacturers offering substantial rebates on their equivalent model 500-600W power supplies, the BFG LS-550 finds itself facing competitors with as good of specs for the same or less cost.
OCIA.net has awarded the BFG Tech LS-550 our Seal of Approval.