The Aruba Instant On 12V power adapter is used to power Aruba Instant On APs AP11, AP12 and AP15.
Order if you with to power with an adapter and have ordered the standalone AP package of the AP11, AP12, and AP15.
Local power is necessary for the remote Access Point if you intend to use Aruba Smart Mesh technology, as Power over Ethernet in that case cannot be used.
Note that R3X85A and R2X20A are functionally identical. Availability varies in different regions.
