The 4 inch (100mm) Nexus Robot double plate aluminium Omni wheels have rubber rollers mounted along its circumference to help avoid slipping. Each roller has two bearings which allow the wheel to move smoothly and easily in ANY direction.
We have a bunch of power supplies laying around. This is a bag of 3 randomly selected 9VDC power supplies (wall warts). 110VAC input. About 6 inches of wire with no ends. If you need a power supply (wall wart), you can't beat this deal.