I have a question regarding AC/DC Power Adapters.  I just purchased an
LCD monitor w/out a power adapter.  It officially needs a 12VDC, 3.5A
to work.  Will a power adapter that supplies 12VDC, 4.0A work
correctly?  Will power adapters rated w/ higher output AMPs work for
applications that require less?

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Request for Question Clarification by mathtalk-ga on 14 Apr 2004 19:51 PDT

Yes, a higher rated power supply means it will work in your
application that requires less.  In fact the spec for the appliance
(LCD monitor in this case) is really an upper bound on current
consumption; most of the time it may draw less current.

The other compatibility issue is the DC plug, generally a recessed pin
on the appliance that fits a round plug from the power adapter.  There
are a surprising number of variations.  With the adapter unplugged,
try the fit.  If it slips into place with a convincingly snug touch,
I'd say you're set!

regards, mathtalk-ga

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Clarification of Question by frozenrubber-ga on 14 Apr 2004 20:55 PDT

That answers my question perfectly.  Unfortunately there are many
types of small variations in the power input plug, and I'll have my
work cut out for me (or maybe i'll get lucky) in finding the right
diameter one (since I can't find any manufacturer specs: Sylvania
L151).  I'll check the polarity graphic as well before I attempt it. 
If the polarity is incorrect between the plug and the monitor, could I
cause any damage or will it just not power?

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Request for Question Clarification by mathtalk-ga on 15 Apr 2004 05:01 PDT

Potentially incorrect parity can damage the appliance (or monitor in
your case).  The variety of plug shapes and sizes is intended to
largely prevent this however.

Awhile back I had a mobile telephone I got at a deep discount because
it was a discontinued model, and it lacked the power adapter.  Radio
Shack had an adapter that came with a variety of interchangeable
plugs, to address the variety of parities and shapes.  Basically they
sold you a base adapter of the correct amperage (and voltage) and then
you put the right "tip" on the end.

They may be able to sort out the right plug for you, if you happen to
live near one of their stores.

Is Sylvania L151 the model number for the LCD monitor?

regards, mathtalk-ga

I feel amperage would matter if you were not supplying enough amperage
for your application. Your 4.0A will work as long as your start up
power is not a lot higher. An automotive battery could have 1000 amp
hours capacity and yet when you turn on the interior light it only
draws what it requires. The same light would not last long at 24v.
What you are going to need to know is with DC your polarity will
become very important, so you will have to get the info as to if the
centre pin is + or -, don't connect until you have that right. Find a
monitor with the adapter and get the info from there, or ask Google.

You should note th polarity of th plug before trying; Some have center
post negative, outside positive; others th opposite. Obviously, your
device and power supply must match.

Spartagus gave good advice. Wrong polarity can destroy. Higher voltage
can destroy. Often a 12 volt device will function with a 9 volt or 11
volt power cube if the amp rating is higher than recomended. Higher
amps does not hurt, except the under loaded power cube will supply
more than the name plate voltage. The non-fitting plugs do not always
save you from distructive voltage or polarity. In the 2 to 10 amp
range some new smaller technology is appearing which may make it even
more difficult to use anything other than the factory replacement.
 I have cut the wire to put a compatable plug on an otherwise suitable
power cube. Going from 3.5 amps to 4 amps is probably safe. 3 amps is
also safe, but the power cube needs to be cooled if it seems unusually
hot.  Neil