@padraig 

TP-Link does not seem to offer power supplies. You can buy third-party power supply adapter with the following specs:

1. Output: 12V 1.2A.

Note that amperage can be higher, i.e., 1.5A, 1.8A and 2A are acceptable. Voltage must be 12V.

2. Proper barrel plug size, discussed here for M9 but in the thread TP-Link Support confirms same size for M5: Deco M9 Plus power adapter barrel plug size

Recommended in that thread: barrel plug size 5.5x2.1 mm