Just recently upgraded to the EVGA 750 P2 in the topic and wanted to share some weird findings between it and the 800W switching PS I was using.
 
When OC'ing my 8700K I noticed that stability was an issue when using the 800W switching PS. Above 5.2G my system was stable at boot and Win10 would boot fine also, but on Firestrike my system would hang during Video test 2. Temps were in the 62-69C range when it would hang. After switching to the EVGA 750 P2, and using the same bios settings/voltages, Firestrike would complete but my temps were a little bit higher in the 72-79C range. I've read that switching PS's operated on specific frequencies and was wondering if the EVGA PS is a switching PS also? I'm trying to understand if my OC'ing findings are a result of the 800W switching PS just running out of voltage, or if it's a function of the switching frequency when considering my OC'ing beyond the 5G threshold..??

Almost all modern computer power supplies are switching power supplies. Stability with a new power supply could be due to a variety of reasons. The EVGA PSU is probably providing cleaner power with less voltage drop. You should also check the voltages provided to the CPU as less voltage drop might supply a higher voltage to the CPU resulting in higher temperatures. 

The original IBM PC used a switching-type power supply.
Outside of laptops the NORM in PC usage is switching and always has been - and even most laptop power supply "cubes" are switching.