Check the polarity and voltage on the router, find a "brick" that matches and isn't obviously a different brand, plug in to make sure it vaguely powers up. Job done. They won't check, it will just go into a skip (sorry WEEE recycling process).
I couldn't see any branded D-Link bricks in my collection (and I have/had at least two D-Link routers). The one that I think came with the router is branded 'Amigo'. I wouldn't be surprised if it varies, with different batches using whichever bricks were cheapest at the time of manufacture/packing. I'd hate to send the wrong one though, and risk jeopardising my warranty claim.
