Can I power a LED controller (Pixlite 4) with a 5V 30amp power supply
Don't worry.
If the device is 5V, and the PSU is 5V too, the device will draw from the PSU only the current that the device needs to work; the PSU will feed the device only with the specific current that the device &quot;asks&quot;.
40 A is the MAXIMUM current that the PSU is able to supply. But if both the PSU and the device are 5V, the PSU will not &quot;force&quot; more current into the device than the device &quot;asks&quot; for.
It doesn't matter if you connect this 5V PSU to a 5V device that needs 1 A, 0.0001 A, 20A, 30 A, or 40 A.
If you have a 3,000 A @ 5V power supply, you can charge your phone with it, even if the phone needs only 1A.
There will be some problems if the device needs MORE than the 40A that the PSU can supply (the device won't work and/or the PSU will overheat or fail).
And don't connect LEDs directly to a power supply. LEDs always need resistors. Most strips of LEDs have resistors built-in, but you should check it before connecting them to the PSU.