hywelg:

Then can you explain to me why your unit (s) put out 12.7volts. Both the ones I own do the same.

These are nominal values, depending on AC power line voltage and load. You do not describe your measurement conditions, so it is hard to comment.

Essentially, you need a minimum PEAK voltage at full load of about 7.5V, and a maximum PEAK voltage under any circumstances of about 15V. You need some expertise and equipment to make these kinds of measurements.

Our power supplies are somewhat over-rated to make sure they function adequately at all times – you will note that while we get complaints about the size, we get ZERO complaints about function – this is important to us.