is power additive?

dear experts:

quick hardware question: is power additive? that is, assume I have a 1A USB 5V adapter installed.

if I now add a standard powered USB 2.0 connection (0.5A) to my (1A) USB 5V cable, does the BBB now have 1.5A?

my hard drive shipped with a y-cable, that presumably helps it to draw 500mA*2. if I connect it to the BBB, can it draw 2A then? (or, if I only connect it, can the BBB draw 0.5A or 1A).



The PMIC chip switches one of the power rails (DC barrel jack, USB port, or the battery connection header) at a time to the internal SYS_5V used to power the 'Bone, so they don't "add".

Full details are in the System Reference Manual (SRM) and PMIC data sheet.