Neither the 3BR, Powerlet or the Burnsmoto USB connector will let my Navman GPS operate in run mode. Pity because the Burnsmoto socket sits under the seat taking up no room at all and a retractable USB cable runs up to the GPS. I don't use it much, so it's no effort to pull the cable and use it on its internal battery if I actually want to navigate with it.
My mobiles are fine and I think my Kindle is OK, although there are other problems in trying to read while riding at high speed or in heavy traffic.
The retractable cable has micro and mini usb tips so that is happy to coil under the seat with a 'phone, so charging things isn't a problem at all. I don't use the 'phone while I'm riding because it interferes with my reading lol.
My preferred outlet is actually the 2 pin sockets sold for marine use, which are vibration proof and fully waterproof, but using one means changing the plugs on everything that you use with it.