Any electronic projects, experiments, prototyping and repair works required an accurate and stable DC Power Supply. There are wide range of bench type power supplies available in most electronic stores and even supermarkets. Determining  which one is best, cheaper and reliable for long use are quite a research task that requires several consideration. 

For an experienced electronic hobbyist, technicians and engineers, choosing a practical bench type power supply may not be a problem since they probably encountered various situations where the cause of the problem was attributed to poor quality power supply. 

Now, how about if a student or someone new in electronics decided to buy one available in a supermarket or hardware store? They might fall into a trap of choosing the cheaper one that looks good on the outside and small. Surely, it will work but the inexperienced person may not have the idea about the quality of the Direct Current (DC) output. Worst is when it comes to poor voltage stability and accuracy  that might ruin their experiments or projects.

As a matter of  precaution to shorten the subject, never buy those cheap square or rectangular plastic cased power supplies with adjustable voltage selector from 3 to 12 Volts DC output for the purposes mentioned above and if accurate DC voltage output is important.  Those type of DC power supplies are commonly called AC-DC Adaptor and comes with single multiple size jack in single plug. 

Below is the basic specification that an electronic enthusiast must take into consideration when burying an inexpensive DC Power Supply:

1. AC INPUT                 -  must be 220 - 240 Volts AC or switchable 110 - 220 or AUTOVOLT from                                                 95  to 260 Volts. 

2. DC REGULATED    -  the voltage setting must not deviate by a maximum of 5% in entire range                                              under load condition. The lower the deviation percentage the better.

3. CURRENT REGULATED - in most cases this is not so important unless for laboratory use.

4. DC OUTPUT RANGE - adjustable from 1.5 to 30 Volts DC

5. CURRENT OUTPUT - must be stable and not temperature sensitive.

6. RIPPLE CONTENT  - this is the more serious one that mostly overlooked or unchecked. Must

                                           be below 20 millivolts, the less the better especially for audio and

                                           video application.

7. SURGE PROTECTION - the main reason why many computers and mobile phones sudden

                                                 failures because some power supplies or chargers does not have

                                                 this surge protection circuit or over simplified. Ever wondered why the

                                                 fuse did not blow after the power supply or charger was damaged  

                                                 or failed?  It is probably due to electrical surge from the main electrical

                                                 supply line that fed your power supply or charger. The electrical

                                                 transient or noise could occur  so fast that it is sometimes several

                                                 times of the allowed input voltage. Imagine what will happen if your

                                                power supply or charger will be fed with a 880 Volts of surge voltage

                                                for 2.5 milliseconds. An ordinary power supply comprising mainly of

                                                diode,  transformer and capacitors  might handle this signal but not

                                                 the more electronic one that uses an integrated circuit (IC) and

                                                 transistors.