4745454b :
750W? It's a 250W part. Not the greatest PSU, but he'll be fine.
750w is what sapphire specs say.
It is probably inflated to consider cheap psus that don't deliver advertised power.
The toxic is a highly overclocked version that takes more than the usual R9-280X
the two required 8 pin connectors at 150w each plus the 75w form the pci slot makes this particular card a 375w part.
It might work, but as you say, the cx is not considered a great psu.