Common rookie mistake to hold the fire extinguisher too close to the fire. Instructors tell you to take three steps back from where you think you should be. Fires can quite literally explode when first attacked with an extinguisher. Better to give it a 'ranging shot' from afar and advance to 'fire for effect'.

The corrosive nature of mono-ammonium phosphate is something to keep in mind when you buy extinguishers. It is less of an issue once there is an active fire. On the other hand an acquaintance once had a fine collection of firearms, some of them museum quality antiques. A minor fire, essentially a trashcan fire caused by a spark from grinding igniting wood scraps carelessly tossed into in a metal bin, caused him to use the extinguisher. He still has the guns but many of them, mostly those not in sealed cases or sleeves, have pitting that eliminated a lot of their value. In retrospect he admits it would have been easy to have simply carry the bin outside, or put it out with the dregs of yesterdays coffee. Evidently is was that small a fire.

Dry-powder ABC fire extinguishers are the number one units sold. The biggest selling points are that they are idiot-proof, no need to know or understand different classes of fire, they are ABC rated, and they are cheap.

They are not the most effective of types for any class of fire. Pound-for-pound most foam units beat the powder on both class-A and B fires. Powder neither cools nor blankets a fire. A class-A fire put out with a powder extinguisher will stay hot, can smolder, and may reignite.

Plain water is often better.

Very old-school but in a lot of situations, buildings with a lot of class-A materials, or where small amounts of grease or oil are the fuel, I would put more trust in a bucket of soapy water or sand.