Play guitars through heavy distortion using a single note at various spots on the neck. Listen for unmusical overtones caused by rattling in the guitar. Spin your guitar around to find the angle with minimal hum. Playing single notes distorts differently than playing multiple notes. Power chords distort more clearly than complex chords.
Power chords have muliple notes, but really only two notes, repeated in multiple octaves.
Some power chords distort more clearly than others, depending on the interval between the two main notes. The Eddie Van Halen tone uses a bridge humbucker pickup. The Stevie Ray Vaughan tone uses a neck single-coil pickup. These principles are known by almost all rock guitarists and producers, who record rock guitar through loud, mic'd tube amps with no loads or power attenuators getting in the way, and only a few effects. There's a general consensus on the Net that speaker distortion is an important factor in amp Tone.