You basically asked the same question over on Worldbuilding. I'm copying my answer to that question here. This answer does not specifically address the strength of the magnetic pulse because whether or not that strength has any affect is dependent on far too many variables to give you a simple answer (e.g., ground conductivity, ground charge, age of the power grid, availability of discharge protection, material used for the wires, climatological conditions, time of day... just to name a very, very, very few). However, it appears you're still looking for a reasonably "real life" justification for damaging personal electronics without blowing the power grid, so the answer is fundamentally the same.
You can screw up wireless coms, but nothing else without destroying the power grid first
The nature of the stellar event doesn't matter. In fact, the source of what's causing the power grids to black out is irrelevant.
What's happening to your earth is a massive magnetic pulse, similar to a nuclear EMP. What's happening is exactly what happens with a generator: a changing magnetic field induces electrical flow in a long length of wire. The long length of wire isn't just important — it's critical. As the wire gets shorter, the strength of the magnetic field must get stronger to induce the same electrical current. The induced current must be enough to either screw up computation (very unlikely) or to blow the device's circuitry (much more likely).
And there's your problem. An electromagnetic (EM) event strong enough to knock out a single piece of electronic equipment would literally cause the wires in the power grid (above ground or underground, unless it was incredibly and therefore impractically deep underground) to vaporize.
OK, so I'm an electrical engineer, but let's not take my education's word for it. Let me give you a practical example. My family used to live in Texas, and one evening lightning struck near our house (yes, this really happened!). The thunder shook the whole house. But what happened electrically?
A phone line (very thin, very long wire) in the corner of the house nearest the strike vaporized. I had to run a new phone cable. All other phone cables in the house were unharmed.
An electrical wire in the wall closest to the strike heated to the point of melting the insulation, which caused it to short out and throw a breaker. I had to pull that and run a new one. All other electrical wires in the house were unharmed. Gratefully, this didn't start a fire, demonstrating the value of sheetrock and uninflammable insulation.
My computer and printer were connected using a 6-foot Centronics-style 36-wire parallel cable. It was just barely long enough to couple enough energy to blow the input port on the printer. The computer was unharmed What this really meant was that the electrostatic discharge (ESD) protection on the printer sucked. Walking across the floor and touching the input port directly would have blown it. I was very disappointed, but back then ESD protection in consumer electronics was only just coming into regular use.
What does this mean for you?
It's impossible to electromagnetically (EM) damage equipment on a global scale without incredible damage to the power grid. All those really long, easy-to-induce-current-into wires make it simply impossible.
However, a strong global EM event could devastate wireless communications while leaving the power infrastructure intact.
