Hi can anybody tell me what adapter I can use 50w charger

http://www.hobbyking.com/hobbyking/store/__14857__HobbyKing_50watt_5A_X_Charger_Balancer.html

in the spec they have mentioned 10 -18 v dc adapter.  But what about amps.  I found different amps in different dc adapter.

I use 12v 5 amp dc adapter for imax b6, got from electronics shop for rs 250.Till now no problems.

For such chargers you can use 1.5A(if you are charging at <1C) to 8A   
Avoid getting a 18v or 17v supply as the charger might get hot!

So can I use 5 amp with 12v dc adapter right

Yes you can! 

This was the one which I brought. But it was mentioned as AC adapter  ? it should be DC adapter. right ?

Even mine came with a crap sticker....yes it should be DC.
To be on the safer side stick in a multimeter and check the voltage by keeping it on dc voltage selection...if the voltage is near about 12V its a DC if the figure is 0V its AC.....most probably its a silly chinese mistake

EDIT:AC oscillates between V+ and V- so in DC mode it should show 0V

It may even show twice the DC voltage too! 

'AC adapter' that doesn't  matter, clearly written output is 12v 5A(and the polarity is inner positive and outer negative) that means this adapter should work.