It was a bit of both, My degree is in CS, I only took one EE/hardware class in school that was more about programming CPLDs than anything else. These days real

It was a bit of both, My degree is in CS, I only took one EE/hardware class in school that was more about programming CPLDs than anything else. These days really all you need to know math wise to build simple stuff is V=IR and P=IV, things everyone learns in high school physics class. Everything else you can usually get by looking at the reference circuits in data sheets or looking it up as you go. The hardest part for me was finding the time to get over the learning curve of the PCB design software, in my case I learned EagleCAD. After I did that and formed good habits with how I used the software I now able to do some pretty complex stuff. The limiting factor now is probably that my ambition has outgrown the software I learned. The niche was building adapters for old server power supplies so you can re-purpose them for use as general purpose 12 Volt power supplies. It was a thing in the RC community for a while to charge batteries but it got really big in the 2014 - 2017 time frame due to the Bitcoin mining industry needing low cost high wattage PSUs.