automotive hu in house

When I was probably about 15 or so I cut a hole in the top of an old house speaker I had laying around and mounted an auto head unit in it to use in the garage. I have since moved out and had forgotten about my homemade contraption until today. It has been sitting in my parents garage on for about 10 years now and hasn't missed a beat. I just took a few min to look at it and remember how dumb I was back in those days and noticed the power supply I used. It appears to be a power supply for something such as a cordless phone or maybe an answering machine (kinda hard to remember those things, lol). Its the typical type of transformer used on cordless phones where the wire is very small gauge and the transformer is built into the plug.   Anyway, its 14v/730mA output. I find it hard to believe that with such a low amperage it would power a HU, however, it has been going for close to 10 years now. What kinda amperage does a HU really draw, and how the heck has my contraption been working all this time?

It'll power it just fine. Will it make the full rated output power of the deck? Probably not.

14V X .73A = 10.22W

That certainly enough input power to end up with a usable output from a speaker. Could be as much as 3 to 4 watts to the driver.