Is it a golden egg?
Back to the original question...
You have one power supply which can supply 3 joules of energy per second (30v @0.1A = 3W = 3 joules per second) and another capable of about 1/8 Joules per second (12V @ 0.01A = 0.12 W = 0.12 Joules per second).
OK, that's a total of 3.12 Joules per second.
What you want is a power supply capable of 360 Joules per second (12V @ 30 A = 360W = 360 joules per second).
so, you have 3.12 j/s in and you want 360 j/s out.
one option is a large capacitor which can store the incoming energy for about 2 minutes, then releases it in a second. This would work with a duty cycle of less than 1% - far less if you need to take into account the practicalities of less than 100% efficiency.
In short, you can't do it because you have insufficient incoming energy (by more than 2 orders of magnitude) than the required output energy.