Case Fan plugged into PowerSupply via 3pin to 4pin molex adapter not working

[NubaBuilder]

Hello, I ran out of Fan Headers on my mitx mobo. It has one CPU fan header and one Sys fan header. The CPU fan header is plugged into the Corsair h105 pump, and the Sys Fan header is connected to the two fans on the radiator. I'd like another Case Fan, so I am plugging it directly into the Power Supply using a 3pin to 4pin molex adapter that I bought from Fry's. Turns out the Adapter says 5v on it.

I dont know why the Fan is not running. I've tried different ports on the PowerSupply, a different Fan (of the same type) but its not spinning. Is it because it's only 5v? Shouldn't it still spin but just slower? This is the adapter I bought: http://www.frys.com/product/2585841?site=sr:SEARCH:MAIN_RSLT_PG

 

[getochkn]

Maybe 5V isn't enough to kick it over.

 

[burdenbound]

yeah I suspect you need a 12V adapter.