This is a device made by Lantronix that adapts a serial port to a network interface. In theory you could plug this into any serial port Atari ST, Amiga, C64, or whatever. On some devices you would need a user port to serial adapter in front of this. Keep an eye out on https://RetroNinja.net to see the trials and tribulations of an Amiga 2000 getting Internet connected.
All of the ones I've seen so far use a 5V@.8A with a standard power jack. If you have a 5V that is rated higher like 3-6A, no worries it will only draw a max of .8A
In general for all electronics the voltage rating needs to be the same but higher amps rarely do.
Some things to keep in mind when you are looking for used MSS100
- look the latest hardware revision, this is listed as F13 here, the hope is the latest revision has the least bugs and most fixes
- look for the latest dated hardware, the 'MFG Date' show 1302, most likely 2013+2nd week