Power Companies are a little bit clever with some of their marketing. After working in the electricity industry there are a few things that you learn that aren't immediately clear about the Power Companies relationships.
To give you an idea, Mighty River Power and Mercury Energy are the same deal. Might River Power is simply the name for their generation arm, and Mercury Energy is the name of their 'sales team'. The reason for this is that they can avoid being cross recognized. For example when it is reported that the boss of Mighty River Power is paid an obscene amount of money people don't switch away from Mercury.
Also the Globug system is completely owned by Mercury Energy and operates in accordance with their rules and policies. The two do work in tandem. Try picking that up from the Globug site.
A little bit more obviously, Pulse Energy, and Just Energy are owned by the same people, with the same staff, with just slightly different colours.
Powershop is a 100% owned subsidiary of meridian Energy whilst Energy Online is a 100% owned subsidiary of Genesis Energy. Again, try finding that information out from their website.
On the last note Energy Online was actually a cheaper independent retailer that was purchased by Genesis Energy. I'll leave you to speculate why this was, and why the prices for Energy Online then increased.