If it only requires 3W, a 15W wall wart should be more than adequate to power it. If you have a car and some jump leads, try it on a car battery.
But it may just be a duff Ebay item, in which a different letter should be substituted for the first S in "Sucking solenoid". I've never heard that expression before, but searching on Ebay brings up a few; all from Hong Kong, so something may have been lost in translation. All are 12v, the first allegedly needing 0.2A for 10Kg and the second (from a different seller) 0.2A for 2Kg. Something doesn't sound quite right there. 12V at 0.2A is 2.4 watts, by the way. I'm no expert on electromagnets, but 2 or 3 watts doesn't really seem sufficient to hold 2Kg.
Contact the seller and if necessary start a formal dispute.
Andy