Take a look and see how many amps the 12v rail is, which should be listed on a label on the power supply. I am guessing you have a single 18 amp 12v rail which is not nearly enough for an A64 and a X1900XT. With one HDD and 1 optical drive, a high quality newer 400W PSU may be fine, because they are starting to make them with beefier 12v rails. Older 400W PSU... not a chance.
For instance, I have run a X1800Xt in an A64 with 1HDD and one Optical on a Antec Smartpower 2.0 400W (ATX 2.0) PSU. It has a 10A and a 15A 12v rail. Compare that to the older Antec Smartpower 400W (ATX) which only had a single 18A 12v rail.
I've never heard of that brand, so can't comment on it. The power looks to be more than enough. Probably be best for you to check some of your local stores for opinions whether its a good brand or not.