I'm not a knowledgeable electronics guy but have occasional need for a simple variable power supply. Probably something in this wattage range would be good. Mainly to control voltage to specific values/ranges where certain devices require specific values. Any features to look for or avoid? One think I don't quite get, some seem like you can set volts & amps independently. Is that thing? Or does the setting mean 'maximum amps' if the device draws what it draws at that dialed in voltage level?