Tariffs for consumers. npower offer a wide variety of plans to their customers, which fall under the categories of Standard, Price Guarantee, Online, Green, and Partnerships. npowerâs Standard variable tariff covers electricity, gas or dual-fuel supply, with the latter offering significant discounts.s such, you should bear in mind that if a new meter is installed, npower will charge you an early exit fee if you switch to another supplier. National Trust Green Energy is npowerâs third Green tariff, and is also one of their two Partnership deals.