If you read the product description, it actually says AC source so simply wiring up an extension cable should work fine. I also find the price to be on par or slightly more by only $1-$2 more shipped. Its way easier to deal with sellers through Amazon than Ebay, the internet wild west...
Part Number 3701WH-12V
Power Source ac
Item Package Quantity1
regarding an LED light for a 30" depth tank, you will certainly consider a lamp that's over 30W for sure.
I get medium /low light over my 20g high aquarium (16" height) with a 20w fixture and most certainly need at least two on this tank.