The PS100, PS150, and PS200 models take in AC or DC power from a wall transformer or a solar panel. The internal regulator controls the charge to the battery to make sure the battery doesn’t become overcharged (based on temperature).
If the switch is on, the voltage from the battery will flow back out from the regulated battery to the loads; however, the voltage on that battery may be 11.9 V, 13.2 V, or some other value that the battery happens to be at. It is important to understand that the voltage will not always be exactly 12.0 Vdc. Rather, the voltage will float up or down as the battery is recharged or depleted.