The first one depends on the motors. For an unregulated power supply I would prefer to use 15...25 V, and use DC-DC converters to make a good 12V for the motors.
The second one is a brandless cheap switching power adapter again. If you buy that, you probably have to buy a better version soon. Don't try to buy a good 12V 4A power supply for 10 dollars, that's not possible.
If you want something cheap, this one: http://www.mpja.com/12-Volt-Power-Supply-85A-100W-Switching-Hengfu/productinfo/16013%20PS/
But I'm not sure how it will behave without any load.
If you want something better: http://www.mpja.com/12-Volt-Power-Supply-51A-Linear-IHN12-51/productinfo/6609%20PS/