The rating on the supply indicates what it can deliver to the device in terms of current. All this means is a connected device requesting current can not ask for any more than 800 ma. The device connected governs how much current will flow, the supply only indicates the amount it can give with out damage or shut down to it self.
Voltage of the supply must be close or exact to what the device requires. In your case you have a 600 ma reserve or power, so you are fine..
"I\'d rather have a bottle in front of me than a frontal lobotomy"
For regulated adapters, you can reasonably assume the voltage will be as stated up to the rated current.
Many adapters are unregulated, however, and the voltage will depend on the attached load. Normally, an unregulated adapter will have the nameplate voltage under the nameplate load, but the voltage will be greater under lesser loads.
If the voltage is "too high" then it may force excessive current into a device, or cause component failure because of the excessive voltage.
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It may work, and it may not... Some crappy designs deliver the rated voltage only at (or near) the rated current, and as current drops, output voltage rises. As such a lightly loaded unit may in fact cause damage because of overvoltage.
Realize that these cheap wall warts are *not* regulated, and the output voltage is approxmate at best in most cases.
"Nominal" means "named", and you check it on the name plate. It is nothing more or less than the promise you're getting from the thing's manufacturer.
You can check the _actual_ no-load voltage at no load with a voltmeter, just by measuring what's on the end of the wire when the thing is plugged into the wall but isn't plugged into the device you want to power.
Control systems and communications consulting
A very frequently asked one, as well. And very frequently answered. Others gave real answers. I agree with the correct ones ;)
Actually, I believe. One kind of adapter that might be able to put more current into a device (by raising the voltage, of course) than is "asked for" is a constant current supply (battery charger for variable number of cells). But it's very unlikely that you have one. The plate would probably have to be wrong, too.
(???) Ok....I'm checking the named voltage as read from the name plate. I'm not sure how I misstated this. There is a voltage it is supposed to be, and I'm checking that supposed-to-be voltage.
You raise interesting (non contentious honest) questions within me noggin. I've heard that voltmeters are not equipped to properly measure a battery's worth because "it will measure the nominal voltage only" which is of course the no-load voltage which also happens to be the named voltage written on the side of the thing. Not sure if the two concepts are yet colloquially synonymous no-load and nominal....I'll trust you on this. But there is an acronym NV.....what would that possibly stand for if the definition were merely satisfied by naming something as "V"?
For an unregulated power supply, like most wall-warts, the nominal voltage is the voltage it will deliver with some load - probably somewhere near maximum currents. With no load other than a meter, the voltage will probably be somewhat higher.
Batteries are a bit different from power supplies. For a dry cell battery, the nominal or marked voltage is the voltage delivered by a fresh battery. A used battery will show somewhat less, even with no load.
The "nominal" voltage of a lead-acid battery or an automotive electrical system is a sort of "random number" only roughly related to the actual voltage. The actual voltage of a fully-charged lead-acid cell is about 2.2 volts, so the "12 volt" battery in your car should measure about 13.2 volts when fully charged, and the voltage of the car's electrical system will go over 14 volts when the engine is running, and the battery is being charged.
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca