Ordered list with capital letters in PowerPoint?
You can do this in the English version of PowerPoint 2011.  


In PowerPoint, go to the Format menu.
Select "Bullets and Numbering".
Select "Numbering" in the right navigation panel.
Choose the appropriate method.




Since there appears to be a difference between the English version and the German version, an imperfect workaround is to use a custom bullet.


This is imperfect for two reasons:


You would have to specify the bullet for every item on the slide that you want to be enumerated as such.  
You can only specify a single character, so you only get "A" instead of "A." for your bullet.  


Using this method, this is what your slide would look like:


You could expand on this idea further, which gets increasingly hacky.  For example, you could create a graphic that consists of "A. ", "B. ", "C. ", ... and then use those as your custom bullets.  Using graphics like this for custom bullets can cause difficulty if you want to update your slides in the future but don't have the original graphic file available.