add2psu is a waste of money. use a piece of wire or a paperclip to jumper the green and black wire on the end of the atx connector. Just be sure not to bond the power supplies together anywhere.(which would smoke the shit out of one or both even with the overpriced add2psu crap)
Also, I have never dealt with seasonic, but corsiar makes a great power supply.
I don't think I'll be comfortable in entrusting $4000 worth of hardware to a paperclip. :-P
I just heard back from the Add2Psu company. They ship worldwide. So availability is not a problem.