My dad has a Skil Drill charger which ain't working. The Trasformer plug output is 17.4V DC 400mA.

The Secondary side of the transformer seems dead.

I was wondering if it would be possible to wire up another Transformer plug to the Charger cradle...which has an output 16V DC 900mA.

If I have the polarity right its just a matter of soldering.

I wasn't sure if the NEW Transformer will output 900mA or will the Battery just draw what it needs. The other alternative is to get one of the multi purpose Switchable Transformer plugs but surely the current will vary on those aswell.

Cheers for help btw

It should be fine.

A device will "pull" as much current as it needs, so there's no problem with having the providing device being capable of producing more current. The battery will draw what it needs.

Also, chances are the 16V output will probably be closer to 17.5V as most non-switching transformers (using primary / secondary coils) are tuned to 220V and not 240V so the 20% voltage increase at the AC side will bump up the DC output

It should be fine.

A device will "pull" as much current as it needs, so there's no problem with having the providing device being capable of producing more current. The battery will draw what it needs.

Cool, I kinda thought that but then one of the guys in work said DC is different to AC in that the A/C would draw as much as needed whereas the DC would push out the rated amount...and overheat battery.