Just for reference, that's a mediocre power supply, maybe as much as the TR-2 430W I recently tossed into the garbage. It's not a 500W unit. It's a ~405W peak (not continuous) unit. It's shuts down ~400W, and the +12V rail is known to drop real low around and above ~310W (that's a stability concern), so it's probably best to say it's a mediocre ~350W unit, but treat it as 300W since it has issues above it, and hey, that sounds much like the case with the TR-2 430W. It won't blow up or anything, but it's a poor unit all around, the TR-2 430's different but yet same twin. In other words, I'd be careful putting such a GPU on it, depending on the rest of the components.
Anyway, if you must do it and stick with that PSU, as mentioned above, I'd get an adapter/converter, not a splitter. Something like this.
Otherwise, you are drawing more power through that wire than was meant, and especially on a unit like that (who knows if they use think gauge wiring too), I wouldn't trust that one. Make sure you ideally connect each molex connector to ones on a different bunch tracing back to the PSU.