As far as I remember the AP80 does not have smart-charging capability. The specs are 5V/2A USB power adapter. Any wall type USB power adapter able to deliver 2A (or more) would do.
Edit: You could check the requirement for your external HD. The same 5V power unit could be used for both player and HD...
Alright, I'll have to check that out. Sadly, my HDD doesn't specify power specs, since it uses the data+power connector usb cable. I'll check the specs and hopefully the internet will have more details. Thanks.