Well... you definitely need to upgrade your PSU. On the website it'll say you need at least 30amps on the 12V+ rail for your card, which you have. But you also power the CPU and all mobo components with that same rail. You're going to exceed your maximum watt output for sure especially when playing games.
To answer your question, the adapters will work fine. I've been using two for almost a year now to run my 460's SLI.