I just used MP3Tag and it successfully gave all of my songs Title tags, but it still shows .mp3 after the song's title, regardless what it is. For example, one song's file name is "Lilypads.mp3", and the Title tag is just "Lilypads", but it still shows .mp3 inside Poweramp.
Edit: another example is I have an album where all of the filenames begin with numbers, but the numbers are not present in the Title tag, yet Poweramp is still showing the numbers and .mp3