I just got my N900 from Amazon warehouse (basically, returned products that they supposedly tested to make sure they work OK).
I am having a problem with the wall charger, which does not charge the device at all. The green light on the charger is ON, but the phone does not respond to that charger at all. I tried it both with the phone on and off, no change at all. I also flashed the device clean, just to make sure it is not a software problem.
The USB cable works when connected to a computer, and it charges the devices, so the problem is not with the USB connector. However, the USB cable does NOT work when plugged into an USB wall charger (which works with my other devices). Any idea what the problem might be? I can't test the wall charger that came with the phone with other devices, due to the fact that none of my other devices have a similar usb connector.

I have a theory: Maybe the wall charger and wall USB charger don't have enough power (they provide about 330mA, while a computer must provide 500mA). Is there any way to view the voltage applied to the USB connector from the device?

Hmm, it seems that now it charges with the USB wall charger, so I guess the Nokia wall charger is broken. I guess it's time to ***** to Amazon a bit.

After I rebooted it (hard reboot, battery off) it again doesn't want to charge via the USB wall adapter, but it charges fine when plugged in a computer..
Did anyone else experience this problem?

problem seems to be with charger itself.

The USB wall charger charges other phones fine, never had a problem with it. BTW, by USB wall charger, I mean a thing that you plug in your wall socket and you can charge any USB devices. Not the thing that came with the phone.

hmm, power output issue than i guess. Did you try plugging your chargers at diff outlets apart from the ones in ya house. It may sound funny but you got nothing to lose.

Your USB wall charger is only 330mA? That is nowhere near enough, the wall charger I got with my N900 is 1200mA, though maybe the USB charger will work if the N900 is idling, but it'll be quite a slow charge and won't be enough when you are using it, sometimes the current from a computer USB port is insufficient to charge the N900 when it is being used.

Another issue that may stop a USB wall charger from working with the N900, is that the N900 expects the data pins on the USB connection to be shorted (connected together) when it is connected to a dumb charger and not all USB chargers do this, but this is (usually) an easy fix if you have a soldering iron and a bit of solder handy.

tusharmax, I put the original charger in two outlets in the same room, and one of the outlets is my UPS, which also feeds my computer, so it should be a very good quality power source (filtered, no random variations, etc.)

retsaw, the wall charger that came with the phone is rated at 5v, 330mA. I also thought it is kind of weak, as it would take around 5 hours to fully charge the battery (if the phone is off). Where are you from? I live in the US, so maybe different areas get different chargers?

I'm in the UK, so the charger will be different, since we have different plugs and voltages, but the output should be the same. Just checking, but are you sure you are reading the output current and not the input current as current is proportional to voltage, so the output current will be higher than the input current.

Yes, I read the output, not the input. Anyway, I didn't read the manufacturer, since I assumed it would be Nokia. Instead, it was Platronics, which is a BT headset maker :/
So I guess the customer who returned the phone to Amazon returned the wrong adapter in the box, and Amazon didn't bother to check. So I sent them an e-mail asking for a proper adapter.