Who has the power

[Spongebob]

I think in your EMP example, the most aggressive/violent group would attain power by accumulating resources. If money were to disappear, currency would emerge in some form and that initial form would be basic resources like fuel, water, shelter...so on. I don't believe many people would be able to avoid aligning with some powerful group or another because there is safety in numbers and anyone left on the outside would be easy picking. That's one thing I believe post apocalyptic stories get right. Picking a group will be a necessity.