Electronic – Extra Current because of Unity Gain Buffer Amplifier

The first buffer outputs a clipped signal between 0.5 - 10 V losing some data by clipping it, which is shifted down to 0 - 9.5 V, still being clipped. The second buffer doesn't modify this in anyway, so to answer your question: the output would still be clipped.

Remember, voltages are only potential difference. Amplifiers reference their input signals to their ground and power supplies, so in order to prevent clipping, you could shift the first buffer's ground and voltage supply up by 0.5 V. I dont see any use for that though..

Edit: I assume you have 10.5V < power supply available for your lever shifter for them to work. Depending what are the power supplies for the buffer amplifiers, they just might pass the 10.5 V without clipping the signals even though datasheet says otherwise.

The op-amp can't do anything useful in this configuration. You need to give it more supply voltage than the desired output voltage, even though it's "rail to rail".

If you ask it to output 8V or even 11V with a 12V supply, it may be able to do that, provided the load is not too much for the op-amp to supply. In this case, that might be 10mA or so.

I don't know exactly why you're only getting 4V at the output, but I suspect it's because the load is something like a couple hundred ohms or equivalent, so the output current is limiting at 20-30mA.

Even if you put a lighter load on there, my first comment applies- this circuit can not do anything useful without some changes (more supply voltage compared to desired output voltage).