The unregulated voltages will be about 10% - 15% higher than the spec. This is due to the wall voltage being higher now than it was back in the 80's. Back in the 80's wall voltage was nominally 110VAC. Today's wall voltage is nominally 117-122VAC. SO that will push the unregulated voltages higher.
This is generally not an issue.
The +12V unregulated on the MPU board is only there to act as a trigger for the CMOS protection circuit. when that voltage drops below a threshold value the CMOS is put into write protect mode.
The issue with switchers is due to a hardware bug in the 6809. WHen the supply voltage drops on the CPU chip, it randomly writes to memory. If that memory is RAM, no biggy, it will be refreshed when the game is powered up next time. If that memory is ROM, again no biggie, you can;t write to ROM. If that memory is the CMOS, you are in trouble. Unless the write protect circuit has kicked in. With switchers, the voltage drops on the +5 volt as fast or faster than the +12 volt (there is more load on the +5V). In that case, the memory protect doesn't have any warning, so it can't kick in.
The Williams power supply was designed with a very large capacitor that can power the +5V for a few milliseconds while the +12 unregulated drops off. This gives the memory protect on the CMOS time to activate and protect your settings and high scores.
That is why it is recommended to rebuild the Williams power supply rather than put a switcher into classic Williams games. Moon Patrol, Motorace USA and MakeTrax use a different design and don't suffer from 6809 hosing.
ken