At least in the case I saw, it has been a few years ago, as I tend to stick to single rails now. My facts may be off, I want to say I set that system up in 2011 or 2012. But I believe the PSU in question was a Cooler Master 460 watt, with 2 18 amp rails. I'd built an amd system, I think it was with a phenom ii x6, 1045t or 1055t. No graphics card or anything special, they were older folks. Just the board, cpu, hard drive, dvd drive, etc. I was working on it and it just powered off, which was weird. So when I ran a stress test on the cpu, it shut off again when I was doing that to diagnose. I put a single rail in it and never had another issue, and haven't gotten any calls about it.
However, I've used dual rails since then if I'm in a pinch, but I tend to prefer the single rail units if I can get them quickly.