Which connectors should I use to connect my Power Supply Unit to the Ramps?
You're quite right :)


L (AC): Brown colour. Single Phase line or Three Phase Line (L1) 
N (AC): Blue colour. Neutral 
GND: Green and yellow colours. Protective earth or ground (PE) 
COM: DC Negative (-) - Also referred to as "Common"
V+: DC Positive (+)
V(ADJ). This is for a potentiometer, in order to modify the output voltage. You won't need this unless your power supply is far off. 


The way to go about these things is to connect the AC side and to connect a multimeter to the output terminals (V+ and COM, there are two of them in case you need to wire up more than one connection). I like to lightly tighten down the probes under the terminals, that way you don't have to mess with the connections with the mains terminals exposed.

Now you can plug in the power supply (PSU) and make sure it doesn't start smoking or sparking. 

Verify that the PSU is outputting DC 12V (that seems to be the voltage required by your Ramps board according to the picture). After that, you can connect it to the Ramps board (remember to disconnect the PSU before rewiring). If the voltage is anything but around 12 V (+/- 0.5VDC should be safe), you need to verify that the PSU is the correct type for your application.