Proper replacement for power adapter?

I have a 6th/7th Gen iPod Classic (late 2009, model number PC297LL, 160 GB). The Apple iPod USB Power Adapter that I had been using to charge it no longer works. It is the square kind with the plug prongs that fold out to plug into a socket. The model number of the power adapter is A1102. (The identifier W005A050 follows that identifier. I don't think that's part of the model number, but I'm including it here, just in case.) I notice that the power adapter was manufactured in 2005, though, so I must have purchased it for my previous iPod and then just continued using it for this iPod. In any case, when I search for this model of power adapter on Amazon, it does not appear as a result (though used ones, some identified as 5v and some as 5w, are available on eBay).

I would now like to purchase a replacement power adapter, one with a power output that is appropriate for and compatible with this particular iPod. Unfortunately, as far as I can tell, the iPod manual does not identify what the appropriate and compatible power output of a charger for this iPod should be. It only mentions that the iPod should be connected to a USB 2.0 port.

Could someone please let me know what I should be looking for? I would prefer the same kind of power adapter - the square kind with the fold-out prongs - but would be fine with just a little plug-in adapter. My main concerns are that I purchase an adapter with the correct power output and that the item is a quality - ideally, Apple - product.

Thanks!

Paul