Here's a quick and simple way to make a Zune AC Adapter without buying the actual one from Microsoft. Basically, you manipulate an existing 5 Volt AC Adapter to support a USB plug. It's important to find the right AC Adapter and to wire it to the right pinouts in a USB plug. I'll cover all of that. What's great about this is that it's actually a universal USB charger since it's equivalent to existing USB ports. If your MP3 player requires a USB cable to charge the battery, then this will certainly work with it.

http://www.instructables.com/id/Make-a-Zune-AC-Adapter/