Some time back I built a card to read all 4 voltages and yesterday took a few minutes to check the IIgs power supplies I had handy. Most I had checked several years ago but there had been some changes. A couple of power supplies are a bit off. I have a +11.5 on one and a +11.6 on another.
Now, what to do? I likely have most of the caps on hand so maybe replace those and see if there’s a difference.
No need to do anything. These are normal values for the +12V rail on all Apple II machines with original power supplies.
The 11.5 one used to be 12.1v
Probably when there had been more load on the +5V rail.
The power supplies in Apple II computers are made to be compact and inexpensive, so they use a "group-regulated" design. The consequence is different output voltages cannot be independently regulated. What you get instead are higher or lower output depending on how much load is put on the different rails.
The overall effect is that instead of a 4-channel power supply, it acts more like a 1-channel supply with a pre-set power split between 4 output voltages. When the loads are close to the same power split, it regulates closely enough. But you can't expect better than ±10% from this type of power supply.
Are you explaining what I already wrote? This is typical for this forum.