The paper {1} that introduced dropout combined dropout with L2:

We found that dropout combined with max-norm regularization gives the lowest generalization error.

• {1} Srivastava, Nitish, Geoffrey E. Hinton, Alex Krizhevsky, Ilya Sutskever, and Ruslan Salakhutdinov. "Dropout: a simple way to prevent neural networks from overfitting." Journal of Machine Learning Research 15, no. 1 (2014): 1929-1958. http://www.jmlr.org/papers/volume15/srivastava14a.old/source/srivastava14a.pdf

The paper {1} that introduced dropout combined dropout with L2:

We found that dropout combined with max-norm regularization gives the lowest generalization error.

• {1} Srivastava, Nitish, Geoffrey E. Hinton, Alex Krizhevsky, Ilya Sutskever, and Ruslan Salakhutdinov. "Dropout: a simple way to prevent neural networks from overfitting." Journal of Machine Learning Research 15, no. 1 (2014): 1929-1958. http://jmlr.org/papers/volume15/srivastava14a.old/srivastava14a.pdf