PC Engine (original) power adapter voltage output

This is somewhat less technical than the original explanation: http://www.apogeekits.com/power_adapter_selection.htm , but I think it was explained pretty clearly in this thread.

If you were being curious for that sake of being curious, that's one thing. That info won't really help you power up your PCE, though.

If you needed the info to purchase a 3rd party power supply, you just have to make sure the specs of the power supply match what the PCE requires. By specs, I mean what it's rated for, not what it outputs under no load. The reason why these two measurements are different and why the output under no load doesn't matter is explained in the link above.