2B Universal Power Supply

It works, much more powerful than the 9 V battery.
Cheaper compatible wall warts can be found on Amazon, without the assortment of adapters.
ADMIN: Yo are correct there are cheaper Mains Adaptors available out there but, the use of an unauthorised Mains Adaptor will invalidate the Lifetime Guarantee and as we ship around the world it is important that we can provide alternative plug options and multi-voltage to all of our customers with one product rather than stock multiple versions of the same thing.