Looking at your figures for the PSU's, the Antec 350W delivers 519.4 Watts, assuming it can deliver the claimed current on all rails at the same time.
The VIP 450W delivers 339.2 Watts on a continuous basis and 459.4 Watts peak.
The VIP 450W therefore would seem to be rated at 450W on peak figures. On the other hand, the Antec appears to be rated on a continuous basis at 350W, but the supply currents given are peak figures which couldn't be sustained.
About time that all suppliers worked to a common method of specifying o/p's, then you would know what you were buying.