To simplify the expression \((19^4)^9\) using the Power Rule of Exponents, we apply the rule which states that \((a^m)^n = a^{m \cdot n}\).
So, we can simplify \((19^4)^9\) as follows:
\[ (19^4)^9 = 19^{4 \cdot 9} = 19^{36} \]
Thus, the simplified equivalent expression is:
\[ 19^{36} \]