Comparison of Eurorack DIY PSUs

A good clean power supply unit (PSU) is the most important part of a modular system. A proper linear power supply and good distribution makes a big difference to the stability and sound quality of the system. Switch-mode power supplies are smaller, lighter, and much more efficient than linear power supplies but produce more noise, (above audio range) on their output.

Safety
Mains voltages can kill and capacitors in disconnected power supplies can still deliver quite a jolt. Unless you're qualified to work with mains electricity, ready made external transformers are safer.