Both can help, but I never noticed enough to make that much difference. Cooked food will probably give you the most, but they only last 5-10 minutes.
The best thing to do is to look at your skills and find the power hogs. Use the power hogs sparingly, or when you know you can kill it before your power runs out. If you're running out of power while soloing, you are going to have a lot of trouble in bossfights, so you might want to look into this.
Teir up.....anthem of composure......coda.....rinse/repeat.......
No more power issues.
It is nice to try and keep anthem of war up the whole time, but i find when i do dailies or quests on my mini while in capstone WS, i kill things so fast that its truly not necessary. Give this a shot and i think you will be happy with the results.