I recently purchased a 30 amp power supply from fellow member Victor_Inox. I am very pleased with it. It maintains voltage, 14.21 or so, even under heavy loads. Has a built in automatic cooling fan and switchable input voltage 120/230. It also features 3 outputs and a indicator light. Victor also ships it with wall adaptor. Nice extra. Almost forgot. As mentioned below the adjustable output voltage did work well. When you adjust, the decrease/increase is smooth and predictable.
I asked several questions before my purchase and Victor answered all of them promptly. I received the power supply within the week after I paid. Excellent customer service.
The price was higher than the cheap eBay power supplies but you get what you pay for. The fact that I own a cheap one and looked elsewhere should tell you all you need to know. It's my understanding that power supplies will be available in different power variations. Have to talk to Victor about that. I only use these for head unit testing and for small amps. It perfoms well and I will be purchasing another soon. Thanks Victor.