Lighting – Are junction boxes needed for LED strip light wiring splices

Regulations vary by country/locale.

IEC SELV is < 25 VAC or < 60 VDC.

See IEEE 802.3 POEP Study Group Safety considerations for POE and POEplus

The more 'electronic' a power supply, the longer it takes to start up. I had this nuisance in my pantry, where I only need light for a few seconds, so I don't want to wait another few seconds every time. I also have a VERY high current demand from a lot of LEDs in total.

I used a sealed lead acid battery on a trickle charger, and a relays. Battery is on common. NO is connected to LEDs. NC to a trickle charger.

Yeah. I'll have to replace the battery when it goes out. Beats waiting for a power supply to ramp up.

Long term, I think I'm going to make a service grade (100-400A) 12/24/48v DC bus for the house, with capacitors for buffering.

You might try a very simple 120vAC to 12vAC transformer (assuming thats your LED's voltage) with a rectifier and capacitor in some enclosure. You're building electrics at that point, so test, and include fuses, etc.