Has anyone used those powered usb hubs with a power connector and noticed an improvement to warrant the extra power plug?
😳 Improvement? You do know why they are used, right?
I am sure you do but, let me explain, just in case:
The USB-bus on your computer provides certain small amount of electric current to all connected USB-devices (with no power plug of their own). If you exceed that figure you are in trouble. When you add an unpowered USB-hub to your computer you are just dividing the current available to more USB-connectors and devices. Powered hub however increases the available current as it does not use the small amount computer is providing but adds its own to the pool.
So, yes - you do notice an improvement after you plug that one too many unpowered USB-device into your unpowered USB-hub that "
breaks the camel's back". Or even one single device that draws too much current. In best scenario only the one device does not work but in many cases the whole USB-bus goes down.
If your USB-device comes with a power plug of its own it doesn't use the bus power to power itself. And then it will not cause the problem mentioned above even if you use unpowered USB-hub.
If your USB-device does not have a power plug of its own it relies on the USB-bus power from your computer. If you have many devices like this (for example an external SuperDrive, USB-hdd or USB-stick etc.) then you need a powered USB-hub (often called USB-switch).
And some tips from Apple:
http://support.apple.com/kb/HT4049
How much your USB-buses can provide current? Open About this mac, more info and USB and you will find the output specs in mA.
So, I hope that cleared things up.
BTW. I just noticed that the iMac sees the Elgato TB2 Dock - USB3 -connections as an actual USB3.0 bus.