...Given what I experienced about Android hardware and software, as well as what I heard about the PSF format, I'm not sure a 2SF, DSF, SSF or USF player would be all that feasible.
Yet. >;)
But until then, there's Droidsound (Available on Google Play). BUT: Be aware of the following caveats:
1. - PSF support's processor intensive, and GSF support hasn't been tested by me yet, but both are the latest two formats added to Droidsound, as of 1.4.
2. - VGM support works in 1.3, but doesn't work in 1.4. (If you're reading this, Jonas Minnberg, please fix this with a proper VGM engine update to the latest version, so we can even support Sega CD, 32X, Neo-Geo, etc.)
3. - RSN support may've been added to its SPC engine in 1.4, but it lists the archives' contents IN REVERSE ORDER!
4. - For those Android users with separate INTERNAL and EXTERNAL storage spaces, there's NO WAY to navigate out of the Droidsound directory in the INTERNAL storage space by default. (If you're this far, Jonas, please add support for browsing the entire file system, short of Root directory.)
Other than that, I think we can manage nicely. ;)
(P.S. - VGMStream support would be nice... *hint, hint*)
Don't forget Lioncash's (one time?) fork of Droidsound with vgmstream support. Not sure if it includes the PSF support though: http://www.hcs64.com/mboard/forum.php?showthread=25115&showpage=0
Rockbox works in Android, but you'll likely have to go to their site to get a working copy. It doesn't support any xSF format, but it does support all the formats of Game Music Emu (also see Google Code for a more updated version. I'm pretty sure Rockbox's GME support is based on the Google Code page. Though, to the best of my knowledge, Rockbox hasn't been updated to include the new soundchips that VGM is supposed to support). Rockbox also supports ADX playback. I don't have an Android device, but Rockbox certainly sounds like a reasonable contender. That said, it seems like Droidsound is actually a good bet right now, but that it needs a lot of detail work for the features to be supported properly (based on what JFD62780 just said).
Anyway, I just felt that Rockbox deserved a mention. You should at least give it a look, to see if perhaps it covers things better for your usage. Mouser X over and out.
As of Sept. 9th, Droidsound has been updated to version 1.4.2. This FIXES VGM support, but ONLY to the point of past Droidsound releases (i.e. BEFORE ValleyBell got involved with the specs. ;)).
...It's a start. Now to work on the other problems... >;)
It's because the dir listing method they're using explictly does not provide any sorting, so if your code relies on that it may or may not work, and it's the kind of thing that could change between filesystems and api levels.