Does the max psi of the booster pump become the total psi of the whole system?

[Mait]

Say the booster pump has a pressure rating of 2.75 bar.
Does the 0.60 bar of the first pump combine with the pressure of the booster pump, making 3.35 bar?

Or does the Booster pump's max psi become the maximum pressure output of the system as a whole?
If so, then why not have just a Booster pump running?

 

[mas985]

Pressure rating is usually from inlet to outlet. However, it is also usually rated at a specific flow rate and that is usually 0 GPM.