One interesting discovery is that you can use a dual plug USB 3.0 cable like this by Lindy for the hard drive: the black plug goes into the Rpi, the red to an USB power adapter. You need to power the disk and the Rpi simultaneously, otherwise the Rpi will suck the power for itself through the black USB plug, something that I believed was not even possible!
Early tests suggest that I should be able to power the whole effectively with three sockets only: one for the switch’s own power adapter, one for this nice Kensington 4-USB charger (although be careful, as the device got lots of bad reviews) and the last for a dual USB charger to which I connect the hdd and the Rpi using it.
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