en plus vs de plus

Question

What is the real difference between "de plus" and "en plus"?  In this writing exercise, the English word "plus" is translated as "en plus,"  "in addition" is translated as "de plus," and "besides" is also "de plus."

Accepted Answer

Hi Adrienne, 
Just to add to what Chris has said, normally at the beginning of a sentence the expressions 'en plus' and 'de plus' mean the same thing. 
I would probably translate them respectively as,  'in addition' and 'moreover/besides'.
To add one more advantage you might use 'furthermore',
which would be probably 'en outre' in French.
Hope this helps!

Answer

It is a mostly difference in register between en plus and de plus: de plus is more formal. Some sources also divine a subtle difference in meaning but that's beyond me.