DC Power Supply specifications

[cruisinto]

I have just purchased 6 Yealink T28P phones and after purchasing I have come to realise that I will need to buy a power supply for each unit separately.

The users manual advises 5V 1.2amp supply however the size of the connection is not specified.

I have come to find out that the 5.5 mm connection would be acceptable however they appear to have two optional core diameters. Either 2.1 or 2.5mm

So in summary my options are

1. 5V 1.2 amp 5.5mm(OD) * 2.5mm(ID)
2. 5V 1.2 amp 5.5mm(OD) * 2.1mm(ID)
   

So which power supply should I use the 2.1 or 2.5 Inner diameter power supply.