So many people are using the wrong external power supply that I need to draw attention to the following.
WARNING: You can't use any old power supply with this Hiface - it MUST be DC output (this will be written on the PS); it MUST have a positive (+) centre pin in the 2.1mm plug; it MUST be between 9V & 12V output & > 500mA current. Please don't try out different power supplies unless they meet these criteria as using a wrong PS is liable to kill the Hiface. Please be very careful here & double check everything!!
A suitable UK 9V DC supply is £14 here but others may well be available locally in your area.
A suitable US 9V DC supply is $10 here but again others may well be available locally in your area.
What you want is 9V to 12V DC supply of 500mA or greater output with a 2.1mm plug with positive centre contact.
You could also run this off a 12V battery using an adapter plug like this or this, again respecting centre pin is positive polarity.
Please be careful with choosing this supply as the wrong polarity will kill the Hiface!