What are "attachments" related to power consumption?

Hardware MikroTik hardware general
1

When looking at the specs for the hAP ac2 I noticed there are two max power consumption ratings. What is meant by “attachments”? At first I thought attachements could be POE out devices but this router doesnt support POE out. Thank you.

Max power consumption 	21 W
Max power consumption without attachments 	16 W

https://mikrotik.com/product/hap_ac2

2

The USB-Interface is the “Attachement” on the hAP ac2.
MAX Power consumption of the USB is 5W (5V x 1A )

3

One up and running gigabit ethernet link consumes about ~1W as well.