The model number of a Mastech DC power supply says a lot about what kind of DC power supply it is. Take for example HY3005D-3, the first two letter "HY" has no specific meaning other than indicating that it's a Mastech DC power supply; the first two digits "30" indicates the maximum voltage it can put out, i.e., 30V; the next two digits "05" denotes the maximum current it can put out in each output channel, in this case 5A; the letter "D" specifies that this is linear power supply (which we will cover later) with LCD display; the next "-3" indicates that it's a triple outputs power supply, meaning you can get three independent outputs, typically with 2 variable and the third one fixed at 5V. Likewise HY5020E means it's a single output regulated DC power supply with 50V maximum voltage output and 20A maximum current output, and it's a switching power supply.