Okay just an update on what I've done so far, powering everything in my arcade cabinet (including the raspberry pi) from one single Power supply.
I made a video of what I’ve done here:
Using the ATX PSU, I made the following connections to it:
5v molex to the Pi (I just cut the pi mains adapter plug off and just wired the cable from the micro USB on the pi into the molex. An expensive option, but I straightforward, and I was getting impatient waiting for a molex to micro USB cable to arrive from China).
5v molex to the NovaGen coin button led
12v molex to the cathode light
12v molex to a cheap 12v 40w car amp. I have this amp connected to 2 10w speakers, and at the moment it's connected to the pi audio jack with an RCA phono cable. But this part of he setup needs work because the background noise is terrible.The amp has an annoyingly flashing LED in it, which is also generating awful noise.
I've got the control panel linked via an ipac2 into the pi usb.
I had an arcade button on there as a momentary switch for powering on/off via the old pic motherboard. I can't really see an option for keeping this. Instead I've shorted the green and black on the psu Sata connector via a latch switch to turn the whole thing on and off. This doesn't allow a "soft" shutdown of the pi, so i will investigate options for this.
I've connected an HDMI to VGA adapter from the pi to the monitor.
A single twin kettle plug splitter cable runs mains power to the monitor and the PSU. The monitor boots when signal is applied from the pi.
It all works well, apart from the noise interference through the speakers.
I've ordered a 180w PICO ITX power supply. It's on it way slowly from Hong Kong. My current PSU is quite noisy, so I'm gonna try swapping it out for the quiet PICO.