So a weak psi can prevent windows from booting and limiting power to gpu,cpu and other devices. like a printer
Not a printer since they have their own power supplies. But yes, a weak PSU can prevent a computer from booting. But a "weak" PSU would likely cause boot problems from day one. So your problem may be a failing PSU.
Note too that PC power supplies supply 3 different voltages, 12V, 5V and 3.3V, to various points inside the computer. It is not uncommon to lose one of those but not the others. So fans may still spin, for example, but the computer might not boot because other voltages are missing.
At any rate, again, because EVERYTHING inside the computer depends on good power, you need to either confirm your PSU is failing or has failed, or verify it is working. And for most users, that is best done by swapping in a spare, known good PSU to see if the same problem occurs, or goes away.
If no spare PSU is available, or you don't feel comfortable digging around inside your computer, most shops will test your PSU for a nominal fee, or even free. Alternatively and though not conclusive, you can also use a
PSU Tester. They are useful for detecting PSUs that have already "failed". However, none of these testers test for
ripple and other anomalies that affect computer stability. And they only provide a little "dummy load", not a variety of "realistic" loads needed for thorough testing. So while better than nothing, conclusive testing is done by a qualified technician using an oscilloscope or power supply analyzer - sophisticated (and expensive!) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. This is why swapping in a known good spare works best for most "normal" users.
