The power supply is for sure not trying to burn your house down. The power supply only provides the power that is needed by the components so if the R290x needs 350w, then the PSU will allow it to pull this power. The problem right now is how much power can the connectors withstand. We are looking into this issue. The power supply already uses high current connectors but if the power draw by the VGA is too high, it is possible even the high current connectors cannot handle the heat generated.
Also please note, our power supplies are all safety (UL) approved so the chance of a continued burn on its own, is very limited.