Building a combined encryption scheme from two encryption schemes that's secure if at least on of them is secure
You can generate a random string $s_1$ as long as the plaintext. Then XOR this value with the plaintext generating $s_2$. Now encrypt both parts using $\mathrm{Enc}_1$ and $\mathrm{Enc}_2$. You need to decrypt both to XOR the two parts together again. This is similar to secret sharing where you need two parts of a key to decrypt.

If $\mathrm{Gen}_1$ and $\mathrm{Gen}_2$ are two random generators then you may want to XOR those together as well when generating $s_1$. I presume however that they are used to generate the secret keys.