Need New Aspire 4720z Power Adapter

Okay, so my puppy chewed through my girlfriend's brand new Aspire 4720z power adapter, right through the cord that plugs into the laptop itself. I have looked endlessly on the internet for a new one, but the variety of adapters/the apparent interchangeability of model numbers has made solving the problem pretty difficult. I attempted to use her old laptop's adapter--which actually fit perfectly into the port--but it didn't charge the computer at all from the wall socket. Basically I can't figure out which adapter I should buy--and not even the Acer website has made the issue any clearer or cheaper. Any help would be greatly appreciated. Thanks!