Some energy suppliers which seem at first glance to be small and independent are actually part of much bigger players from the UK and further afield. Did you know that not-for-profit Ebico is a partnership with Robin Hood? That Ovo Energy owns app-based Lumo? Or that Npower is the driving force behind Sainsbury's Energy?
If you're concerned whether a new entrant will stand the test of time, it might reassure you to know it has a big backer. But if you were hoping to take your custom to a small local provider, you might be disappointed.
We also found that the prices vary between brands with the same company backing them - and it's not always the core brand which is cheapest.
Keep reading to find out whether your small supplier is part of a bigger group and how to get the best prices.
The cheapest prices on the market are often from small brands. See the in our monthly round-up. Smaller and newer brands are also often the ones which are digitally-focused, or offer innovative tariffs and services first.
But bigger brands have stood the test of time and may have the financial backing and experience to hedge their prices long-term, helping to give customers price stability.
In light of several smaller energy firms going bust in the past few years, we're often asked by Which? members if smaller firms, newer firms, or firms they haven't heard of are 'safe'.
And it's not just small firms which get into trouble or change hands. Economy Energy went bust last year with 235,000 customers, while was acquired by Ovo through the supplier of last resort process with 290,000 customers.
Plus Npower is now majority owned by Eon, with Npower in debt and making a loss on its household supply business for the last few years, according to regulator Ofgem. SSE is selling its energy services business to Ovo, after it got the go-ahead from the Competition and Markets Authority (CMA). The deal will complete in January 2020.
Some energy firms enter the market as small players and are subsequently bought by bigger firms. Others may be acquired when they get into trouble, for example through the supplier of last resort process.
Other brands are launched by bigger firms - or subsidiaries of them - trying something new. That can include pricing.
Here we give you a snapshot into smaller brands, and who is behind them. Click on the name of an energy company to find out which brands it's involved with:
One of the six biggest energy firms and former incumbent, Npower has a subsidiary you probably haven't heard of called PS Energy Trading. This has several trading names.
Npower supplies the gas and electricity to customers of the firms but they use a different operating system, called Flux, to manage their customers' accounts.
Powershop says it's a new kind of supplier, 'not like the big companies' and bringing a way of buying energy that's 'loved in Australia and New Zealand'.
The Powershop brand originated in New Zealand where it isn't small either - it was backed by one of the biggest suppliers, Meridian Energy.
Sainsbury's Energy used to be backed by British Gas, but now PS Energy Trading is its supply partner. That means that Npower supplies customers with gas and electricity but Sainsbury's Energy's website, customer service and bills use the same systems as Powershop.
Prices between the brands differ. The cheapest deal is from Sainsbury's Energy and costs £53 less per year than Powershop's cheapest deal and £94 less than Npower's cheapest deal, when we checked in December.
But Npower's tariff for out-of-contract customers costs £1,179 per year so customers could save £206 in a year by switching to Sainsbury's Energy's cheapest deal.
Octopus Energy is a fast-growing firm with more than one million customers and backed by an investment firm (Octopus Investments). One reason it has grown so quickly is that it has acquired other energy companies, including the following.
Affect Energy's website says 'we're based on the south coast, in a lovely little town called Shoreham-By-Sea'. Customers can still pay their bills on the Affect Energy site, though Octopus bought the brand back in September 2018.
Co-operative Energy recently became a partnership with Octopus Energy in which Octopus Energy supplies customers with gas and electricity and manages customers' accounts. Co-operative Energy is still responsible for gaining new customers. Originally, it was launched by the Midcounties Co-operative in 2011.
Flow Energy and GB Energy both begun life as independents, but later became part of Co-operative Energy. GB Energy Supply went bust in November 2017 and Co-Operative Energy took it on. Flow Energy became part of Co-operative Energy back in May 2018.
Now all of their customers are with Octopus Energy.
M&S Energy was originally a partnership between the retailer and SSE. But the two parted company in September 2018 and Octopus became the supply partner. Octopus Energy supplies customers' gas and electricity and customer service, while M&S Energy manages the brand and is responsible for marketing.
The cheapest deal across the brands was Octopus Energy's, costing £920 per year, when we checked in December. It cost £270 less per year than the cheapest deal from GB Energy.
Co-operative Energy's cheapest deal available in England, Scotland and Wales cost £75 more per year than Octopus' cheapest deal so customers can get the same service for less with the owning provider.
Ovo Energy is the biggest independent brand. Since launch in 2009 it has been the supply partner for several council energy companies, as well as setting up its own ventures. They all operate on the same (Ovo's) license to supply gas and electricity but have different customer services and pricing.
Boost is the dedicated prepayment brand of Ovo, originally called Ovo pay-as-you-go. It has a dedicated customer service team.
Digitally-focused Lumo allows customers to compare their tariff with 'the whole market' in its app. This is the only way customers can interact with Lumo; it doesn't have a traditional call centre you can phone. Though not immediately obvious, Lumo's terms and conditions reveal that it is operating under Ovo Energy's supply license.
In fact if you don't comply with Lumo's eligibility criteria, 'we'll have to change you to a dual fuel energy plan operated by another company operating under the Ovo Energy Ltd supply license'. An example of non-compliance is if you agree to pay by direct debit but then cancel it.
Spark Energy is also part of the Ovo Energy family, after it got into financial difficulties and Ovo took on its customers.
It retained the brand, along with its customer services team based in Selkirk.
Lumo sold the cheapest direct debit payment tariff across it, Ovo and Spark Energy, costing a medium user £160 less per year than the same customer on Spark Energy's cheapest tariff.
Lumo's tariffs aren't available to customers in north Scotland however.
Meanwhile Ovo's cheapest deal cost £88 more than Lumo's cheapest tariff.
Boost's prices aren't comparable as it sells prepayment meter tariffs only.
A previous version of this article, published on Friday 20 December, incorrectly stated that Robin Hood Energy is the supplier for privately-owned Yorkshire Energy. There is no link between the two companies. We sincerely apologise for any confusion caused by this error.
Robin Hood Energy was set up by Nottingham Council in 2015. Since then it has expanded, including becoming the supply partner for around nine councils which have set up their own energy firms. These include:
This means that Robin Hood Energy buys and supplies gas and electricity to customers on behalf of the councils. It also provides customer service, complaints handling and some marketing for the brands. Meanwhile, the councils create and market their energy company brand. They are paid commission by Robin Hood for signing up customers.
The price of all deals sold across these suppliers varied by £544 per year for a medium user when we checked in December. But apart from Ebico and Robin Hood Energy, the brands only supply customers in certain regions. This means that prices are affected by the different costs for the region.
The cheapest price was offered by Ebico, Robin Hood Energy and the regional brand in each region.
Several other new energy firms might seem small to the untrained eye, but are in fact part of much bigger firms, based outside of Great Britain.
Engie, Enstroga, ESB Energy, iSupply Energy and Orbit Energy all have less than 1% market share here. But they're much bigger fish in other markets.
Engie is a global energy supplier and generator, which joined the UK market in 2016. It's also behind Qwest Energy which is a partnership between Cheshire West and Chester Council and Engie.
ESB Energy is Ireland's state provider (called Electricity Supply Board). Set up in 1927, it is majority owned by the Irish Government and supplies electricity to 1.4 million customers across the island of Ireland.
iSupply Energy has been around since 2012 and was bought by Vattenfall in June 2017. Vatenfall says it is 'one of Europe's largest producers and retailers of electricity and heat'. Besides the UK, it operates in Denmark, Germany, the Netherlands and Sweden. It is owned by the Swedish state. Find out what customers think of .
Orbit Energy is owned by an Australian investment firm in partnership with US Genie Energy.
Prices are based on a dual-fuel tariff available in the regions stated, paying by fixed monthly direct debit, with paperless bills.
Energy use is based on Ofgem's annual average figures for a medium user (12,000kWh gas and 3,100kWh electricity per year).
Data is from Energylinx. Prices given are averages across regions, rounded to the nearest whole pound and correct on 11 December 2019.