Hello again,
Yes, the transformer resistance can play a part in the drop in voltage too, but that also depends on the output cap ESR and also
the leakage inductance causes a drop too. The diode drops have a part in it as well. Depends how cheap it really is i guess.
I agree however that the resistance might play a large part in it sometimes, but remember that the highest peak is due to the
sine peak and when the cap is charged to that value it is highest, and as load is added any ripple with always bring the
average output down even with less resistance. Maybe with extremely large capacitance and low ESR that wont be as bad.
Also, as the power supply ages the ESR goes up which makes the peak loading issue even worse.