What size power supply do I need to connect two 5 meter LED strips?
It says 2.1 amps/5 meters for the 30 LED/meter strip, 4.2 amps/5 meters for the 60 LED/meter strip. So, that's either a 5 amp @ 12V supply or a 10 amp @ 12V supply.

I would not recommend hooking up the two strips in serial; the LEDs at the end of the second strip will likely be much dimmer than the ones at the beginning. You can get around this by running a thicker cable in parallel with the strip.