Well, there is always the chance that the adapter is putting out more than 12v. Most of them do, and many of those only use half wave rectification or do not have a filter capacitor. Put a big (220uF - 1000uF) electrolytic capacitor across the adapter and measure this 'filtered' voltage. Be sure to observe the polarity and the voltage rating of the capacitor. The capacitor should be rated at more than 16v.
The delta V method varies depending on the internal resistance of the battery. It is most effective for large, low impedance batteries like those used in tools. Smaller, high impedance batteries, like those used in cordless phones and other low power electronics tend to float higher while charging and the delta V is not as sharp. Especially if the adapter you are using as a source has a low voltage. Remember, the diode and regulator are going to drop the input voltage by a minimum of 2.5 volts (and another 1.25V across the resistor, if you get things running), leaving you with only about 9.5 if indeed that adapter puts out only 12V. This is not enough to effectively charge your battery.
So, do the test I mentioned above and let us know what the resulting 'filtered' DC voltage of your adapter is.
You really do need at least 16V or this circuit will not work. If you can't get 16V, then I would recommend just using a resistor to limit current and cutting off the charge when the battery gets to 10.4V. The exact value of that resistor will not be known until we know the exact filtered output of your adapter.
Edit: By the way, I do not recommend you using a bridge, or anything else, to rectify the power coming out o the wall. What is the AC supply voltage in Malaysia? 240? Please don't try to power this thing off 240V directly. Very bad things will happen.
