I've always thought that a car audio amplifier would be best for the job of sound in an arcade cabinet. The problem is, it seems no one makes the small but high quality car amplifiers like they did in the 80's and through some of the 90's Remember the Rockford Fosgate Punch 30? 15W x 2 @ 4 ohms. Even when small high quality amps were being made, they weren't cheap. Right up until about the mid 90's, quality amplifiers were a couple of dollars per watt at least. Using the Punch 30 as an example, given that its power would be 30W x 2 @ 2 ohms / 60W x 1 @ 4 ohms, it would be considered a 60 watt RMS amplifier and sell for a bit over $100 back in the day.
So when power became cheap, first down to a dollar a watt in the late 90's and a good deal cheaper than that now, the small high quality amps were kicked to the curb. That makes it hard to recommend a car audio amplifier for an arcade cabinet these days because about the smallest you are likely to find that is of high quality is 50W x 2 @ 4 ohms (200W x 1 @ 4 ohms), and those require more juice than a typical PC or arcade power supply would care to give out. Plus they are still relatively expensive, usually a little over $100 for that size.
So anyway, I was on Dave Navone's site today looking at line drivers and I came across a little 20W x 2 @ 4 ohms car audio (12VDC) amplifier (
http://www.davidnavone.com/linedrivers.htm "AMP-100" about halfway down the page). Dave Navone is a legend in the autosound community, and many top competitors use products he invented/designed/built (read about him here -
http://www.davidnavone.com/about_navone_engineering.htm)
You can be sure this is a quality amplifier, and it won't put much strain on a typical arcade cabinet power supply. In addition to the typical low level inputs (RCA) it also comes with high level (speaker level) inputs, which is another thing you don't see too often these days. That means you could use this amp to easily upgrade the sound in a dedicated arcade machine by running the speaker wires into it as an input.
And it is only $40.
BTW, I am not affiliated with Dave Navone in any way, even though I might be coming across as a salesman. It is just that I've seen a lot of threads asking about car speakers (or any speakers for that matter) in an arcade cabinet, and they usually end up hacking some cheap PC speakers, which typically don't have quality amplifiers at all.