Electrical devices grill her toast on Sunday (9)
I believe the answer is:
rheostats
'electrical devices' is the definition.
(rheostat is a kind of electrical device)
'grill her toast on sunday' is the wordplay.
'grill' indicates anagramming the letters.
'on' is an insertion indicator (as in clothing \'on\' a person).
'sunday' becomes 's'.
'her'+'toast'='hertoast'
'hertoast' anagrammed gives 'rheotats'.
'rheotats' going around 's' is 'RHEOSTATS'.
(Other definitions for rheostats that I've seen before include "Current regulators" , "They alter resistance" , "controllers of resistance" .)