DIY 5V power supply from phone charger
Given that you at looking to use it at 75% of it's rated capacity, you should be good to go. USB chargers are ubiquitous as basic 5V switching supplies.

It will work, given you buy a decent/reputable usb charger and not a cheap knockoff of questionable quality. A decent charger will have proper isolation between the mains side and the dc output, as well as safety features like a fuse or Over Current Protection. A cheap one may not actually put out 2 Amps.

Keep in mind that some chargers will put out slightly more than 5V, to make up for power loss over the cable. This would benefit you. You want to use a quality cable as well, with thicker wires. Cheap wires may use aluminum instead of copper (or copper coated aluminum) and of a smaller cross section, resulting in higher power loss at higher distances/current.