The other issue with GPS supply voltages that a lot of people miss, is:
Although the GPS electronics actually run off 3.3v (in most cases) the expected supply voltage is 5.0v and there is some sort of crude regulator.
I say “crude” because
a) there’s very limited board space
b) supply voltages below 5.0v start to affect actual GPS performance
And consider that is with new GPS modules. Good luck with the older ones and a poor power-brick!
Or cheap copies…
And consider the 4.7v supply (meant to be about 5.2v) from a cheap power brick goes through at least 1 connector to get to the flight controller, probably two connectors, then another two connectors from the flight controller to the GPS unit. Add in the resistance of those connectors, some noise and ripple, it’s a wonder the poor GPS units work at all.