Most efficient way?
Well, on the PC: player.additem 00075FE4 100
gaming.stackexchange.com/users/15092/SaintWacko
Here are the different ways I've been able to find fusion cores so far: Merchants - At least a couple merchants I've come across sell fusion cores.
This currently appears to be the easiest way of obtaining cores if you have the caps.
Fusion Core Reactors - Not sure if this is the right name but they are big light green generators (like the one you use to get a fusion core in the mission where you meet Preston Garvey) and are found in many buildings throughout the Commonwealth and always give 1 fusion core.
The difficulty in obtaining cores in this way varies but if you're an avid explorer
you who searches every building (like me)
you should have a good stockpile of cores in no time.
Power Armor - At least a couple of Power Armor suits I've come across have already had at least a partially charged core.
Since you only need to power one suit at a time I make sure to take the core out of suits I'm not using.
Also, if you equip a companion with power armor they will need a fusion core but don't seem to drain it so it's best to just give them one with low charge.
Sentry Bots - These guys are pretty rare and super hard to take down (the one I encountered was hit with 2 mini nukes and still had to be finished off with a laser rifle), but they drop 2 fusion cores and some other goodies.
Theoretically, if they respawn somehow you could farm them for cores (albeit at a cost of ammo and stimpaks).
Random Places
- I have been able to find a few cores in random containers or just lying on a table or the ground
but it's very rare.
High tech or military related buildings and locations seem to have a better chance
but I've also found a few in people's houses.
Not sure if the chance of finding cores is increased with luck or with some perk
but it's definitely worth investigating.
As far as the most efficient way to get cores, I think that depends on your play style.
Just exploring as many areas as I can has worked out pretty well for me; but if you're more charisma oriented then getting a deal on cores from merchants might be best, or if you're focusing on combat then tracking down sentry bots or other rare, hard-to-kill baddies could net you a good amount of cores.
As a bonus, here are also a few things you can do to extend the life of a core: Repair
Bobblehead
- Found at the top of the Corvega Assembly Plant, it permanently increases the duration of your fusion cores by 10% Nuclear Physicist
Perk
- With each rank it increases the duration of your fusion cores.
At full rank it doubles the lifespan of your cores.
Fusion Core Reactors???
- I've heard a rumor that placing a core back into a reactor and pressing the button next to it will allow you to recharge the core.
I haven't tested this myself
but if true it could help alleviate the issue of finding cores in the first place.
gaming.stackexchange.com/users/130162/WeaselNinja
Well I will say researching this question was actually pretty hard surprisingly.
Based on what I have learned you can buy them from some merchants so that would probably be the most efficient way to acquire them if you have the caps to buy them.
I have asked a couple people if there is a way to produce them from base building and they stated that they hadn't seen one yet
but they did say that they haven't discovered everything regarding bases yet.
So as of this time it seems finding them and buying them are the only 2 ways to acquire fusion cores at this time, of course we may learn of more methods in the coming days.
I know it may be an incomplete response but its better then not getting one at all
I hope this helps you.
gaming.stackexchange.com/users/129270/Nightmare
You can easily find fusion cores by pick-pocketing them out of the suits worn by Brotherhood of Steel Knights.
gaming.stackexchange.com/users/131368/zeolacy
When I maxxed out the scrounger perk and had a high luck stat, I was able to loot them from regular boxes from time to time.
I don't know that it's the most efficient means, but it seems to have helped.
gaming.stackexchange.com/users/135026/Bartleby
What is the most efficient way to acquire fusion cores to power Power Armor?  Power Armor suits are plentiful, nearly everywhere, on raiders and sometimes just locked up in a cabinet.   The issue is that fusion cores, the items you need to power them, just seem so rare, or the ones I find are always low on power.  What is the most efficient way to acquire fusion cores?
Most efficient way to acquire fusion cores to power Power Armor?
gaming.stackexchange.com
<fallout-4>
gaming.stackexchange.com/questions/242547
gaming.stackexchange.com/users/18916/korrasaur
You can buy them from some merchants or pick-pocket them from the suits worn by Brotherhood of Steel Knights. Few ways to acquire fusion cores efficiently is either by buying them, from merchants, or pickpocketing the Brotherhood of Steel knights.
The community suggests few ways to obtain fusion cores.