Wow, is this not the most useful thing you did not know existed or what? Its a switching wall adapter where you can easily change the voltage! It's like a benchtop supply you can take with you anywhere.

This model is 10 Watts and has 6 selectable outputs ranging from 3V to 12VDC and up to 1.5A output. It has a 2-prong plug, but takes 110VAC to 240VAC so you can use it anywhere with a simple plug adapter.

It comes with a range of tips, such as 2.5mm mono, 3.5mm mono, 5.5mm/2.5mm, 2.5mm/2.1mm, 4mm, etc. You can also change it from center positive (most common) to center negative (less common but seen in some audio gear) You could use this with just about any device or project, it's very handy!
 

Technical details

• Multi changeable plug DC-cord.
• Universal AC input 100V to 240V, 50Hz/60Hz
• Universal AC input plug available (BSI, USA, Europe, Aust)
• 6 selectable outputs: 3V-12V MAX. 1500mA.
• Over load, over current, over heat protection.
• International approval CE EN60950, UL1950, CSA22.2 No.950.
• EMC approval EN55022.
• Extra low consumption during standby (about 8% of linear adapter).
• Small size: 67x29x74mm.
• Cable length: 1.54m / 60 3/4"