This should be under the Graphics forum section.
However, I wouldn't push that PSU too far. If 400W is the minimum required, I wouldn't want to run it on a 400W PSU for very long. You'd essentially be pushing your PSU at 100% of it's capability all the time while gaming. This will create a lot of heat, and stress for that PSU. That could lead to a fairly short lifespan.
It's best to upgrade to a better PSU so it's not running at 100% capability.
The other thing to consider, is whether that PSU is rated @ 400W max output, or is actually capable of 400W consistent load. Those two figures are not always the same.