Increasing USB port Power Output

I have a new (2013) 15" Macbook Pro.

The USB port provides 500mA which is not good enough for many devices I use (Hard Drive, 3G Dongle...)

Reading this article: http://support.apple.com/kb/HT4049 it seems that these ports are capable of delivering more power, but it's limited to Apple products.

Is it possible to hack the mac, and change this default value (to something like 900mA?)

Apple USB 3.0 ports will output up to 1100mA if requested, USB 2.0 is limited to 500mA

You can check the current requirements for any attached device in Apple Menu > About this Mac > More Info (later macOS versions now labelled 'System Report…')... USB

I only have USB 2.0 ports on this machine, but see pic...

Thunderbolt or USB hub

You can fix this by using a powered USB hub. This way you do not have to modify your mac.

This Belking 4-Port USB hub for example.

The only negative, you need a power socket.

Another fix is to use a Thunderbolt hub, like the Matrox DS1. This is a hub with Thunderbolt input, needs no additional power, and outputs all sorts of IO, including USB 3.

Another possible solution, that avoids any sort of hacking, would be to use a USB-Y cable. These cables provide two usb connectors that plug into your laptop and merge to a single cable that's plugged into your external device, therefore pulling current from two usb ports on your laptop. Many external HD's come with these, they're inexpensive, and do the job. See http://www.toshiba.com/us/accessories/Cables-Adapters/Cables/USB/BA-82010 for an example.