The Raspberry Pi 3 is powered by a USB Micro power supply that can supply at least 2A at 5V for the Model 3B, or 700mA at 5V for the earlier, lower powered models. Lower current (~700mA) power supplies will work for most basic functions, however are more likely to cause the Pi to reboot if it draws too much power.
Using an adapter such as 1528-1798-ND above will allow you to use a wall adapter with a 2.1mm ID and 5.5mm OD barrel plug to get 5V and 2A and properly power your Pi 3B.
Here is a list of Barrel Plug Power Supplies Digi-Key carries that will work with adapter 1528-1798-ND and provide 5V and at least 2A.
Great post! I see a lot of people in other communities asking about power supplies. Also good to know that you can just buy an adapter like that instead of the specific power supply Adafruit has. Sure the Pi is $30, but after all the accessories you’re at $60+. The adapter costs less than $2
Globtek has a wide range of 5V power supplies with MicroB connectors for Raspberry Pi applications. They come in many shapes and sizes, current levels, and also medical and non medical one’s depending on where they will be used. All of them are UL or NRTL certified as well as internationally approved: Digikey Search | GlobTek
By the way, Raspberry PI 4 requires a 3A power supply with a USB Type C connector. the GlobTek WR9QA3000USBC-CIMR6B and WR9QA3600USBC-CIMR6B fit the application well with WR9QA3000USBC-CIMR6B offering an exact 3A rating matching the requirements and WR9QA3600USBC-CIMR6B offering a robust 3.6A for extra power, cooler running, and longer life span. Both offer high quality industrial cables with rugged USB type C connectors. All these adapters feature a multiplug system with 9 accessory blade options covering the entire world. The multiplug blades are sold separately providing a lower cost solution and less waste in unused plug options. The product is also certified to multiple international standards such as Medical IEC60601-1, Household use 60335-1, and ITE 60950/62368 providing new opportunities for implementation of the Raspberry Pi system. They are also globally certified for North America, Europe, and many Asian countries.