power chords are easy you can take either the first 2 strings of any chord or the first 3 example

Em
e---0-----------------
B---0-----------------
G---1-----------------
D---2-----------------
A---2-----------------
E---0-----------------

E Power Chords
e--------------------
B--------------------
G--------------------
D---------2----------
A---2-----2----------
E---0-----0----------