Forgive me if I sound completely ignorant, as I'm not well-versed in power supplies. I've been thinking about purchasing a 610w PC Power & Cooling PSU in preparation for a video card upgrade (http://www.newegg.com/Product/Product.aspx?Item=N82E16817703005). This PSU has 49a on a single 12v rail. I've recently read that it may not be safe too have such high amperage on a single rail, due to the risk of a short causing a fire, melted wires, or other damage.
Is this something to worry about? For that matter, what could cause such a short to begin with? Apparently plenty of people use these PSUs with no problem, and they're very highly rated, but I'm just trying to be safe.
Too much power through single rail... That's what they were worried about in the olden times, so they required artificially splitting rails. It's been a long time since then, large single rails will work fine. Don't worry about it.
The amperage on a rail only tells you the amount of power it potentially can deliver. And a shortcut with 5 amps will melt something just as it would do with 25 amps; if the device fails and thus doesn't shut off it's the same...
Just as the others said, make sure you've got a good quality device and you'll be fine.