Review on Pack of 9 UCEC MB102 3.3V/5V Power Supply Module for Arduino Nano Solderless Breadboard - Enhanced SEO by Scott Hadlock

These are really practical plug-in power supplies. Removing breadboards can even be useful offline. The selectable dual voltage is handy, and while the regulator output isn't perfect, it's more than enough. I measured the 3.3V line at 3.23V. An installation note: make sure you attach it to the breadboard so it aligns properly with the power lines. Otherwise, you'll have to remember that they're swapped, or move your circuit around (if you built the circuit before adding the power supply and left room on the wrong side, as I may have done). It is not a replacement for a quality desktop computer. PSU, but more than adequate for desktop experimentation and cheap enough to be built into even simple projects that are a step ahead of breadboards.