Friend turning up with excellent computer (6)
I believe the answer is:
laptop
'computer' is the definition.
(laptop is a part of computer)
'friend turning up with excellent' is the wordplay.
'friend' becomes 'pal' (pal can mean a friend).
'turning up' shows that the letters should be reversed in order.
'with' is a charade indicator (letters next to each other).
'excellent' becomes 'top' (top can mean the best).
'pal' written backwards gives 'lap'.
'lap'+'top'='LAPTOP'
(Other definitions for laptop that I've seen before include "Portable computer" , "Kind of computer" , "Some work on this" , "Type of computer" , "Aid for businessman" .)