Hi,
To answer this question, in March 2015, there was a global announcement that the iPower would be shipping with the powered iFi devices. This included a price increase among other things, to reflect the upgraded power supply.
Hence as you purchased after March and as you paid the new higher price, then you should receive the iPOWER.
As you are in England, just PM us with information of your retailer and any receipts you may have. We'll chase up for you.
It would not be fair if you paid the higher price but did not receive the iPOWER. We'd be more than glad to sort an iPOWER out for you.
Cheers.