The problem with a CME, of sufficient size, is that it will dump so much electrical energy into the earth's natural "ground state" aka the green wire that you will end up with the effect of everything shorting to ground. The 1859 Carrington Event shorted out telegraph lines, exploded batteries and dumped enough energy into the infant electrical grid that they removed all the power sources and used the electrical flow of the event to power everything for about a week.
Don't think of it as a shockwave, instead think of it as running 50,000 amps through a 12 gauge wire. Where Cletus shorted the ground to the hot leads.
Now, imaging the same level of energy input but this time you have a trillion dollars worth of very intricate transformers, power stations, long distance high tension lines and nowhere to dump the extra energy and not enough time to shut everything down. Each of the super transformers, we are talking boxes like these things are custom jobs and they don't have extras lying around. One goes boom and they make a new one. Normally, you get electrical trouble on the grid, you short to ground and then fix the break. Now, imaging THERE IS NO GROUND and shorting to ground increases the flow into the system. Now you have thousands of very expensive, hard to replace intricate high tech devices to replace, each one taking 1-3 months to make and a month to transport. Oh, and the factories that make these things? No power. The materials processing factories? No Power. And the ships, trains etc? No power. And with "Just In Time" logistics, everyone has 3-5 days of supply on hand, if that. Then, the water systems start to fail, refrigerated food stocks start to go bad and the supermarkets are empty. Maybe you could sever the grid and save some of the power distribution if you had 3-4 days warning. Nuke plants need time to shut down. You just cannot flip a switch and turn off a coal burning plant. And the 2012 CME made it to the earth's orbit in less than 20 hours.
Our electrical grid in the US is shit; it's 40 years old and held together by hopes and good feelings. It needs a near full upgrade so that we can push hard for non-fossil fuel power sources. It also needs to be modernized so that things like the 1989 Quebec Outage and the recent Northeast US Power Cascade can't happen. But that requires lots of money and a functional government.