My Master System 2, will run off my Mega Drive 1 power supply quite happily.
I've no idea how similar the MS1 and MS2 power supplies are though, so that may be useless information for you.
It would probably have been fine really but given the age I checked the bottom of the console.
9v 850mA for the Maaster Sytem
10v 1.2A for the Megadrive
I cooked my Disk Doctor drive a few years back overvolting the shoddy regulators they used

 
	 
  
 
		 
 
		
 
 
		
 
 
		 
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