Can i upgrade a chasis 6506 with a sup720-3B + WS-X6724-sfp + WS-X6148A-GB. What is the difference between the chasis 6506 and the 6506-E
You need to upgrade to a "high-speed" fan tray (WS-C6K-6SLOT-FAN2) and your power supplies need to be 2500W or higher.
However, the 6148A card will see no performance increase. These cards are built with an 8 to 1 over-subscription, and are intended for wiring closet applications.
There are some enhancements to the backplane in the E chassis, and they can support more than 4000 W of power.