Your adapter on ebay has a female plug(the little black one). It does not seem to be made for a normal fan. If you look in the link to the Evercool fan, the third picture is what the adapter should look like.
To be honest, most fans i have ordered came with the 4 - 3 pin adapters.
I actually have a similar question I've been wondering about. I would like to add this fan to my side-case mount and I'd like to put it on its highest setting via molex, but still hook it up to the mobo for fan speed monitoring, and lower speeds when idle, etc. But I'm not clear how that works with the connections.
Is this a "one or the other" thing? Where I can either hook it up to molex for maximum power going to it? OR I can hook it up to the mobo for variable speed? Can I do both?
Product details say:
3-speed switch lets you balance quiet performance with maximum cooling
3-pin and 4-pin power connectors provide convenient connections to your motherboard or power supply
Fan-speed monitoring capability included (requires compatible motherboard) http://store.antec.com/Product/cooling-tri_cool_fan/tri...