Yes you get x % of your ACTIVE companions stats - cant remember what the % is and I am at work right now - I think its 16% for one legendary companion.
So if that companion had 1000 power you woudl gain 16% of this = 160 extra power
SLightly off topic - you only get the % of the ACTIVE companions stats dont you?
So its not worth slotting rings and stuff on your NON active companions is it to build their stats?
You have 1 SUMMONED companion. That's where you put runestones and gear
You have up to 4 ACTIVE, NON-SUMMONED companions. There is no benefit to putting gear on those - although you can store unwanted gear on them - basically use them as free inventory slots, but you gain no stats or benefits from doing so. Those companions only give you their active bonuses.
Finally, you can have a number of NON-ACTIVE (idle) companions, and again...it is pointless to put anything on them.
Answers
So if that companion had 1000 power you woudl gain 16% of this = 160 extra power
its a buff icon on your char, not a passive bonus.
No powershare
You can find a list of what counts as base power or not here : https://arcgames.com/en/forums/neverwinter#/discussion/1227832/reference-power-sharing/p1
So its not worth slotting rings and stuff on your NON active companions is it to build their stats?
You have up to 4 ACTIVE, NON-SUMMONED companions. There is no benefit to putting gear on those - although you can store unwanted gear on them - basically use them as free inventory slots, but you gain no stats or benefits from doing so. Those companions only give you their active bonuses.
Finally, you can have a number of NON-ACTIVE (idle) companions, and again...it is pointless to put anything on them.