hello,

can i use a 24V - 2AMP instead of a 24V-1.5AMP for a RB711 board ???

Of course, you can!

24V is "fixed" voltage, and 2A is MAXIMUM amperage the power supply can produce. How much of the amperage is actually produced - depends on the device connected to the power supply (it is proportional to the power in Watts). So you only have to worry to have proper voltage, and not to have too weak amperage . The more powerfull device you have (board, number of wireless cards), the more amperage the power supply must be prepared to give.
And, of course, needed amperage also depends on voltage. Power [Watts] = Voltage [Volts] * Amperage [Amps]. So 24V giving 2A produces the same power as 48V giving 1A (which is 48 Watts) .

thank you dasiu....