Can the Arduino do this - power source switch

That was quick
Was just about to switch of for the night
Not much to tell really but info below. At the moment I'm only using the solar panel's and they work well when in 'full' sunlight, which is why I'd like to have the transformer power as an alternative.
Any help gratefully received

Hardware
Two 6v solar panels wired in parallel
per panel
Power: 2W
Working Voltage: 6V
Working Current: 0.33A (330mA)
http://www.ebay.co.uk/itm/6V-330mA-Solar-Panel-Solar-Cell-2W-2-Watt-136x110mm-Pi-with-Diode-CLEARANCE-/221419043742

WATER FOUNTAIN PUMP KIT LOW VOLTAGE MAINS POWERED
Mains Plug : 6v 300 mA
Operation Voltage: DC 6 Volt