Rudolf and Matthias like to play regular power chordes (E D A etc.). I think they usually match the tuning of the guitars to the abilities of klaus to sing the songs.
One more thing, Rudolf and Matthias play the songs for so many years so if klaus have dificulties to reach the higher notes they would prefer to tune their guitars down to Eb drop D drop C etc.
If you will look at Matthias' gear you'll find out quickly which tuning He chose to play the songs:
Dommenget Black Explorer 90 with the stars is ALWAYS tuned to drop D ! (don't let the video of raised on rock mislead you it's Eb tuning there).
Other guitars (especialy Mastercasters but not only) are tuned to Eb (Coast to coast, Still loving you, Deep and dark, when they played with Michael Schenker etc.).
Until 2005 klaus was singing Wind of change and You and I with standart tuning. At that time Matthias played with his Jabocaster (E tuning) those songs. Today you will not find any song that is played with a regular E tuning.
Also Matthias has some Explorers with other tunings like drop C (for love'em or leave'em or hour 1 etc.)
As for Acoustica all the song are tuned to Eb except Life is to short and When love kills love that tuned to Db.