A couple of the right electric substations hit could make things unpleasant.

Saudi ARAMCO?

PRM2 said:

I couldn't agree more, unless the drones are autonomous and relatively sophisticated, they will be very vulnerable to RF noise jamming (the inverse square law really comes in handy here), if deployed against any advanced force

I would be concerned that the future drone design would operate like a HARM anti radar missile, where it automatically homes in on and attacks the source of the jamming signal. 

Farmplinker said:

A couple of the right electric substations hit could make things unpleasant

Seems like that was recently attempted:

https://www.thedrive.com/the-war-zone/43015/likely-drone-attack-on-u-s-power-grid-revealed-in-new-intelligence-report

Good point, that is the difficulty with ECM/ECCM and home on jam, however there are counter tactics that can be devised and it would hopefully negate the use of simple mass produced grenade droppers. More capable drones would be larger and heavier with high power demand and probably easier to detect and counter with other measures (maybe CAWS has a use after all with the addition of a smart optic). They would also be too expensive to use regularly in swarms (although potentially useful for one off stunts).

Hahaha, that’s a good one.

On the one hand, it's a crushing, devastating and transforming blow.

On the other hand... a sizeable number of UAS can be quite catastrophic

RF jamming is a shield nice for the threats of the past. sUAS are already capable of being independent from remote pilot. Now the first line of defense is GPS spoofing

Absolutelly. Now think about dozens of substations

It depends what you are dealing with, GPS spoofing is an excellent countermeasure against sophisticated autonomous drones, but it wouldn't affect the simple manually controlled grenade droppers, hence the need for old fashioned noise jamming or other countermeasures too.