Not about computers, but nutsy boltsy. Smart people here, in my experience...

[eppur_se_muova]

19. OK, 200mA refers to the maximum current, and is the same as 0.2A (Ampere).

Multiplying the voltage (20V) and current in A (0.2A) gives you the power in Watts, which is 4W. This is the maximum your device will consume.

The old adapter was marked 8.5VA, i.e. volt-amperes, which is the same as watts. So the adapter could draw as much as 8.5W from the power line.

You need the voltage to be the same -- 20V -- but if the adapter can provide *more* than 4W, that's no harm -- you're just paying for a bigger adapter than you really need. Most of these laptop chargers are way more powerful, like 40W to nearly 100W. If you bought one of those it would be "underutilized", to put it mildly, but it should work. You don't want to use an adapter that is TOO SMALL -- that would overheat and even catch fire ! Better surplus power available, than drawing more power than it can deliver.

So any adpater that can deliver 20V and at least 4W output should do. You may not even save any money by buying a lower-power adapter, since they are mass-produced for laptops at low prices. Matching the plug will be your biggest problem for now.