Powder Fire Extinguishers, such as ABC powder extinguishers or dry powder extinguishers, are suitable for fighting class A,B and C fires.
ABC powder extinguishers have a very good fire fighting capacity, but the powder does not soak into materials and does not have a good cooling effect on the fire.
This can result in the fire re-igniting, if it is not properly extinguished. Care must be taken when using powder extinguishers that you do not inhale the powder.
Powder extinguishers should therefore not be used in small, confined spaces where there is a risk of inhaling the powder. In fact the British Standard does not allow powder extinguishers in offices and living accommodations any longer. The clean up after applying a powder extinguisher is also very difficult and the powder causes damage to soft furnishing, carpets and computer drives etc. So a careful balance has to be struck between the generally quite cheap but powerful powder extinguishers and the cleaner, but less powerful and sometimes more expensive foam/water (with additive) extinguishers.
For a household be careful not to buy just BC rated powder fire extinguishers, as they generally are not suitable for burning solids. BC rated powder extinguishers, however, can be used for cars.