Hello, Matthew.
I am not sure how well paralleling the U3V50F12 boost regulator would work. In general, we do not recommend connecting regulators in parallel since it is difficult to ensure their voltages match and that the load is distributed evenly across them. It is much better to use a single regulator that can provide enough current. For your application, it sounds like a single U3V50F12 boost regulator should work.
When you were testing your setup with a power supply, how were you measuring the voltage and current of the regulator? If you were using a multimeter, it might not have been fast enough to see the regulator turning off momentarily when it was near its current limit. I suspect that the momentary shutoff might be responsible for turning your computer off. If you have access to an oscilloscope, you might try measuring the voltage and current to see if the regulator is turning off. Did you try powering your computer with just a single regulator and your battery pack? Have you consider using a larger battery pack (e.g., 2s or 3s LiPo)?
- Jeremy