Purchased an Xbox 360 power supply at the thrift shop for a few dollars. It has a relatively powerful 14.2A 12V output. It is basically a computer power supply in a portable ruggedized kid-proof casing. For the Xbox 360 there are 3 versions: 16.5, 14.2, and 12.1 amp. Others have reported converting them to general 12V power supply use.
First step was to cut the factory dc plug off. When you plug the power supply into AC power you will get an orange LED. To enable the 12V output connect the red and blue wires together (the LED will change to green). You can wire them together permanently or even switch it electronically and have a remotely controllable dc power supply.
The voltage is a bit low @ 12.2V, but is acceptable and does not drop too much under load. As far as noise it is surely not in the same league as a proper (much more expensive) power supply. However, I have tested it briefly on the HF bands and was still receiving quite a few signals. It's definitely superior to other low-cost switching power supplies and 12V chargers I have tested. Should work great for VHF and above. May not be ideal for 24/7/365 application, there is a variable speed internal fan which would probably fail after some time. Still, considering the cost, it makes a decent portable or spare/beater 12V power supply.