Actually it's 9VAC or 12VDC @ 500mA or more, but if you want to phantom power a MIDI controller, you need more than that. 1000mA is enough for most controllers, except the Rocktron All Access. With that one you'll need 2000mA. Conveniently, the All Access comes with a 9VAC 2000mA adapter that works quite well to power both the RG-16 and controller.
And the most important thing is: don't use 9VDC!