Well, it may be reliable enough for use, but it may not be a good power supply, and might falter after awhile, or if you load them up enough.
MOST computers don't come with a high quality power supply, and alot of complaints are caused by cheap power supplies. But that doesn't mean everyone who owns a cheap power supply will run into problems with it. In fact, most people don't run into problems with cheap power supplies.
If you're willing to run that risk, then your original PSU will do.
As with FSP, I've never read any reviews on them, never seen any sort of highly methodological testing on them, and I have never seen the insides of one, so I shouldn't comment on them. So I will comment on the Antec, of which I own a few of my own, and have been proven again and again on highly methodological testing.
Bear in mind that the Wattage is just an indication of what the PSU might do in a cheap power supply. As in, it is POSSIBLE for it to reach 400W in a cheap power supply. Some cheap power supply independently test each rail, and add up the Wattage, which is just stupid because you will not just use the +12V rail, or the +5V, or -12V or whatever, but all of them at the same time. However, in good power supplies, the rated Wattage is the maximum average Wattage which can be sustained by the PSU. A cheap PSU on the same testing as a good one will be rated much lower.
Hope that clears things up.