The USB Charging standard was discussed on another thread, and one very important fact was mentioned. It said that almost word for word..."phones using this standard should start arriving in the US in early 2012."
This means unless your phone was designed and manufactured to meet this new standard AND (OH SO VERY IMPORTANT), the CHARGING BLOCK WAS ALSO MANUFACTURED TO THIS NEW STANDARD, then AND ONLY THEN, can you depend on this standard. In other words, just because a new standard has been agreed upon doesn't mean that now every phone and charger out there meets this standard.
In fact, Motorola RAZR and RAZR MAXX are NOT compliant to that new standard.
There are MANY threads about phones acting strangely when plugged into a non-Motorola charger block, and yet there many very intent posters who are saying that all you need to be sure of is that the voltages are within range.
I say, all you need to do is ask yourself why that charger makes the screen go berzerk when the stock charger doesn't. There has to be something different which causes the phone to be unable to properly communicate with the digitizer.
Since the only thing that moves from the charger to the phone is power, and since there's only three measurements, volts, amps, and waveform (or quality of power), the problem has to be from one or more of the three. Voltage fluctuations are not likely since the wall voltages are fairly stable and that translates into stable step-down voltages. There are also capacitors in place to further stabilize volatges. Current fluctuations aren't likely since again wall current is also fairly stable, so the current limiting circuitry will do its job and there should be little if any fluctuation. So what's left? How about regulation, i.e. dirty power...remnants of the AC waveform at high frequencies, harmonics for those who understand that concept, and RF interference, components which can actually impart "noise" into the voltage signal much like static on an AM radio.
These wall adapters have a very tough job in total. Initially they have to take harsh and dangerous voltages of around 110VAC US (220VAC Europe) and reduce them to a tame 5.1VDC @ +/- 5%. Reducing voltage is the easy part. It can be done the old fashioned way, with a transformer by having the proper ratio of windings on the opposing sides of the iron core and using the magnetic field set up by the windings on the high voltage side to excite the windings on the low voltage side and impart a reduced voltage flow thorough those windings. With a different number of windings on one side versus the other, you get a different voltage on one side than the other. The greater the difference in windings, the greater the difference in voltage. It's really elementary. There are new high-tech ways to accomplish the step-down in voltage by using timers or "switching transformers" but the result is the same.
That in itself is unfortunately only a very small part of the process. Now you have to convert the alternating current coming from the walk into direct current. This is no small feat. You have to take what looks like a roller coaster ride from the beginning of the climb at the bottom, to the top and then down to the bottom of the fall and back up, and turn it into a perfectly flat line. How this is done is what sets an approved charger apart from the rest. All you have to do is look at what that power looks like on an Oscilloscope and then you would understand what I mean. If it's properly filtered (regulated), the voltage would appear as a perfectly flat line sitting right on the 5.1V position on the screen. Even a fairly well regulated supply may "look" flat, but if you increase the Oscilloscope's frequency sensitivity range, you may begin to see tiny little spikes and drops. It's this ever-so-small "static" or "noise" that can be at the root of this problem.
Since the digitizer is measuring a change in capacitance at the screen surface (the difference between the ambient charge between the anode and cathode of the underlying capacitor junctions), and since these changes, how ever slight they may be are enough to indicate where your finger is, if there is a change in the voltage due to dirty power, the digitizer interprets that "noise" as finger-presses all over the screen, and you wind up with "ghost typing". On the other hand, if the power is clean and free of artifacts or remnants of the AC ripple, or noise from the regulator circuitry, or RF interference that manages to leak into the circuit, then the digitizer only "sees" the change in capacitance at those junctions when your finger is really there.
This is why the stock charger doesn't cause interference with the digitizer yet others do. Case in point, check out this thread (
http://www.droidforums.net/forum/dr...properly-when-plugged-into-computers-usb.html). This is a USB port on a computer, which is supposed to be 100% USB compatible and so should be 100% compatible with the RAZR, and yet it is producing dirty power and affecting the digitizer on his phone.
Also, regarding current and using a charging block that puts out more than the recommended current (i.e. 750mAh or 1A for rapid charging), such as the 2,100mAh mentioned, the phone SHOULD be able to limit that current to the battery. However if the charging circuit which limits that current should fail, and you're plugged into a charger that puts out 2 Amps, you could have the battery suddenly receiving that full current and the battery may begin to heat up rapidly. This could result in damage to the battery or more. Why take chances? If nothing else, charging with a high-current supply will only shorten the life of the battery. Yeah, it'll charge faster, but the battery will start taking less and less of a charge faster too.
Better safe than sorry with a phone that retails for in the 3/4 of a Grand...use the STOCK charger and avoid using any other charging source if at all possible.
