Electrical Requirements and Current/Voltage Ratings
Connectors don't "carry watts", they carry current.

Current rating of your connectors has to meet or exceed the design current of your circuit. This is to prevent overheating of the contacts and excessive voltage drop across the contacts.

Voltage rating of your connectors has to meet or exceed the voltage difference between adjacent pins and between the pins and anything else in close proximity.


  Is it safe to assume that I could use a power supply of 48V and 5A, ...?


Definitely not.