Hello,
For a few years all the Apple monitors were powered off the tower, so a custom dvi connection that included power and usb was used called the "Apple Display Connector" as the previous poster noted. I'm not saying it was a brilliant idea, but it accomplished a design goal of only one cable coming out of the monitor.
Here's where to get the correct adaptor. It includes adc>dvi, plus a power supply for the monitor and usb breakout. It's larger than you think.
Apple DVI to ADC Adapter - Apple Store (U.S.)
Hugh