Does a bigger capacitor cause a lower voltage?

But yes exactly, because more charge is stored on a bigger capacitor, in a given amount of time and with the same load current the bigger capacitor will discharge by a smaller fraction compared to a smaller capacitor. This means the voltage across the bigger capacitor will go down less. (This actually follows from your V = Q/C equation.)

Does increasing capacitance affect output voltage?

From the formula of charge relating capacitance and voltage, Q = CV, capacitance is inversely proportional to voltage. This is how I got the idea that possibly when increasing the capacitance, the output voltage would decrease for both buck and boost converters.

What happens if you put a smoothing capacitor on a converter?

Putting a smoothing capacitor across the output (i.e. with the other side of the capacitor connected to ground) of such a converter will cause the capacitor itself to charge to the output voltage.

Can a capacitor supply current to a converter?

Thus, in the periods where the converter cannot itself supply current (i.e. when the converter is charging up the e.g. inductor inside it), the capacitor can supply current to the load instead.

What happens if you increase capacitor size to 100 UF?

Observations (using a 5 V peak AC signal input): If I increased the capacitor size to 100 uF and leave the resistor fixed, I get a smoother (more DC-like) voltage. However the value of this smoother DC is now 4.1 V, which I find strange. Shouldn't this DC voltage be exactly the same as the 4.4 V peak that was obtained using the 1 uF capacitor?

Does a larger capacitor decrease the output ripple for a fixed load?

A larger capacitor will decrease the output ripple for a given fixed load. First, on your equation: your logic isn't right because Q, the charge on the capacitor, isn't fixed. What the equation in fact says instead is that for a given output voltage, a capacitor with more capacitance C will store more charge on its plates.