This is a helpful way to view it. Apple's 2016 revenue of 215B was about 0.2% of gross world product (GWP)... Which means the power draw if extended globally would be 5x our current global use. Of course, it wouldn't actually happen that way, because Bitcoin itself would then cause the price of power to increase.

Edited: fixed mis-use of "world GDP" to GWP as per tantalor's comment below. Thanks!