Confusion in deriving ripple voltage for an unregulated power supply
Here's a picture from a different web source that gives the same answer but, notably with small print at the bottom: -



So it's an approximation and it doesn't take account of diode drops either: -




  What is the real ripple Voltage here?


This picture is better because it shows the forward volt drops in the diodes but it's still not exact - how far do you want to go getting to the real answer. Do you want to consider any of these: -


Non-linear resistance of the "real" load
Real load effects such as pulses of current it might take
Self-discharge of electrolytic
Transformer secondary leakage inductance and resistance
Volt drops in wires


It's just an approximation at the end of the day and at the point when the formula becomes grossly inaccurate it's probably a good idea to add more capacitance to the bridge output to reduce ripple voltage anyway!