ErQCOLA2016 Basicly you have two types: 1) Fixed voltage, mostly 5V or 12V usualy used for ledstrips where the leds are connected in parallel. You can attach as much leds your power supply can deliver. The more leds the more current is needed but the voltage stays the same? 2) Fixed (constant) current, often 300mA. Here we have a serial connection of the leds. The number of 'led-bulbs' you can connect is limited, if each led-bulb needs e.g. 36V then the power supply must provide 108V when 3 of them are connected, if you connect two of them then the voltage will be 72V. In both cases the current is 300mA. For constant current supply the minimum and max voltage is important. Lets take the "8-25W:DC60-90V" model and a 36V 300mA Led-bulb. The minimum power supply voltage is 60V, when you connect ONE Led buld it will be destroyed. When you connect 3 of them they won't light up because the requered voltage of 108V can't be reached. So this combination is only for 2 led-bulbs.