I’ve just switched to Extra Energy (in the south of England region). They are supplying my existing Economy 10 meter (and times) with their Economy 7 tariffs quoted.
Bright Fixed Price Tariff until Sep 18 
Very helpful and didn’t require an explanation. It does vary though, as I phoned last week and was told they didn’t support Economy 10. Apparently they have new staff who are learning, so they apologised.