Advantages of RG59 Siamese cable are:

• both video and power in one cable
• Video run in RG59 Coax cable  
• Power run through 18 guage pair 
• Cable can be cut to exact length  
• Works with twist-on, crimp-on, and compression BNC connectors  
• Can be run up to 1000ft without amplification  
• Heavily shielded to minimize interference  
• Available in Black or White. 
• The advantages to using this cable is that its more durable, and you can run it long distances without interference.
• Also, you can cut each camera run for the exact length that you need If you are using a camera with audio or a  PTZ camera (which requires a data cable connection) you will need to use a special type of RG59 which includes an additional data wire in the jacket.
• The RG59 Siamese cable is more heavily shielded so it's more durable and can be run longer distances (up to 1000 ft. without a repeater). It's heavier shielding makes it less susceptible to interference. Florescent lighting in particular can interfere with camera signals. The RG59 is purchased in 500 or 1000 ft. rolls and each camera run is cut to the exact length needed. Since you need to cut the cable and attached the connectors, it is a little more involved to install.

Freeport Security provide DC connectors with extension wire making it very easy to power your cameras.

DC Connector For Bulk Siamese Cables