Some Fuzz-Face derivatives (the '69 is one of those) use NPN transistors and a standard tip-negative power supply. Others use PNP transistors and require a tip-positive supply. But sometimes they can include what is called a "charge pump" - a magical chip that can provide a +/- supply from a + input, or a negative supply from a positive input, or a higher voltage supply from a +9V input. Verify what your '69 pedal requires, and adhere to that.
Some pedals will run cleaner with a higher-voltage power supply, because it gives them more headroom. And some, like the OCD will simply run "differently". In the case of pedals that use op-amp chips and clip via diodes to ground, many gain settings will push the chip past its headroom limits and result in clipping within the chip itself, the chip's output is then clipped a second time b the diodes to ground. Raising headroom via a higher supply voltage will raise the headroom of the op-amp chip. It won't completely eliminate any clipping within the chip, but until you move the gain/drive control above 12:00 or higher, most of the clipping will come from the diodes, only becoming a "double clipper" at much higher gain settings. You may like that, or you may not. Clearly Bluesrocker does, which is neither good nor bad.
Some pedals actually DO run "better" at higher supply voltages. I have a couple of old Boss BF-1 flangers, which can only run off external power (they would kill a battery before the gig was over). The chassis says 9VDC, but the service document with the schematic says 12VDC. In that particular case the pedal does run better, largely because the additional voltage allows the sweep to be perceptibly wider.
Just as fewer volts sometimes, but does not always, bring out the best in a distortion or fuzz pedal, MORE volts does not always improve a pedal's performance. There is nothing especially "magical" about +9V. But the majority of pedals are designed to perform quite acceptably, using a 9V battery or equivalent supply. "Good enough" might be improved upon, or may bethe best the circuit actually can do,