Dynamo (yellow) increased tenfold at the outset (5)
I believe the answer is:
demon
'dynamo' is the definition.
(I've seen this in another clue)
'yellow increased tenfold at the outset' is the wordplay.
I cannot quite see how this works, but
'at' could be 'on' (location) and 'on' is found within the answer.
The remaining letters 'dem' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for demon that I've seen before include "Fallen angel" , "malignant spirit" , "Skilful person" , "beast" , "Ghoul" .)