You might not want to use a portable water fire extinguisher on live electrical equipment. But you might want to use a hose. NASA did a study on computer fires. Burning printed circuit boards are hard to extinguish. NASA's conclusion was to use water. The water stream breaks up and does not conduct electricity well and besides the water in the hose is grounded. Maybe the water on the burning boards conducts, but that causes the circuit breakers to blow. The water provides cooling which is what is needed. The Navy came to pretty much the same conclusion and uses low velocity fog nozzles.
Dan