“There are many power supplies which are suitable for the Raspberry Pi computers, but it is often found that using an aftermarket one does not supply the amps specified by the Pi or even printed on the aftermarket power supply.
I found this out the hard way and had problems with a Raspberry Pi throttling (slowing down the cpu) to conserve power, and random crashes on a couple of my early applications, switched to the genuine power supply and it cured them all for good.
Moral of the story - Always use a genuine Raspberry power supply.”
“This is a must in my experience with pis’ to date. The small pi zero tends to be happy with any power supply but the 3 and 4 variants are fussy and give voltage warnings if the correct power supply is not used.these from the pihut are not over expensive and work perfectly.”
