How many devices can I connect, and can I use bigger power supply?

[pistein]

Hey,
I know very little about electronics and such, so I have a newbie question.
I have a Pi where I want to connect several additional components. Sense HAT, camera, maybe 3 or 4 other sensors via USB.
What kind of considerations do I have to make in regards to power to the devices?
How do I calculate how much I need, and when it is too much.

And is the limitation on the power supply or the Pi? Can I just buy a bigger power supply?

[topguy]

No you can not "just" buy a bigger power supply, there are still limits to the chips inside the Pi about how much power they can deliver to outside units.
HATs are usually not a problem, they are constructed to the Pi specifications and if they need much power they have their own power socket.

USB is the main problem, but here the simple and recommended solution is to buy a "powered-USB-hub" that way the USB devices dont draw any power directly from the Pi.

[klricks]

For a RPi 3B the total current used by all USB devices cannot be allowed exceed 1.2A
The current consumption of the entire RPi, when powered by the mircro USB port, cannot be allowed to exceed 2.6A
There is no point in getting a power supply larger than 2.5A.

[W. H. Heydt]

The input power circuits of the Pi limited the maximum current draw. This is a safety feature. Pretty much the only reason to use a PSU rated at more than about 2.5A would be if you were unsure that the PSU was robust enough to maintain 5v output at that load. In practice, that means that going *moderately* over the maximum that the Pi can use can be justified, but it is not wise to go a lot over it, as a truly high powered PSU could simply overwhelm the the current limiting circuits on the Pi if something were to go seriously wrong.

Personally, if concerned, I wouldn't go over about 4A. In practice, I use PSUs from vendors I trust to supply good ones, such as the RPF PSU.

[Imperf3kt]

Use an ATX power supply like the kind found in your coomputer. Check the max amcurrent rating of the PSU and don't exceed that.
This way, you can have a 5v rail power your Pi and a 12v rail power other devices. If these devices require 5v, simply add a buck converter (keep an eye on efficiency!)

You can buy brand new single 5/12v rail PSUs at ~400Watts for $25USD