Correct.
Any connected device could be the problem. That is why so much of trouble-shooting is to simply narrow the problem down to one particular device, one cable, one situation, one person, whatever.....
What makes things even more confusing is the failures are intermittent (sometimes happen, sometimes do not). Or one part of a device will work and another part will not.
If the card reader is not getting power then it could be the outlet, a bad plug, the power supply, an internal power problem, maybe just the power to the memory card slot. Could be the electrical is all good but there is some physical wear and tear that inhibits good firm electrical contact.
And many card readers are low quality to start with: after some time and use they start failing. Even little power failures/interuptions (for whatever reason) while writing to the memory card could corrupt the card. And many devices are being made to fail at some time or the other. Add in cheap components, substandard manufacturing methods, limited or no Quality Assurance it is sometimes a wonder that anything works or lasts.