A PC power supply, it will run off 12v (Yellow 12v and Black ground) wires.
You should always aim for double your requirements to get in the most efficient power band.
Hex16B are about 50w each. If you bought 4 that's 200w, get a 400w PSU for best efficiency.
Where to get a HEX16B
http://technobit.eu/index.php?id_product=52&controller=product&id_lang=1Typical 400w PSU
http://www.scan.co.uk/shop/computer-hardware/all/power-supplies/computer-psu-atx-power-supply-unit-300w-530wCheaper PSUs tend to be less efficient and have annoying noisy fans that run full speed all the time.
Also if power efficiency is important spend the extra 37 euro on the TL-MR3020 router with preloaded CGminer /dd-wrt it will save having a PC/Laptop on 24x7 which cannot beat 1.5w!
TL-MR3020
http://technobit.eu/index.php?id_product=37&controller=product&id_lang=1Note the Wifi is disabled you will need to hook it up to a wired network connection.
Accessories you may need are USB cables and a USB hub (if you are running multiple Hex16B's)