Right, but if the charger causes damage to components on the bike, this is not covered under warranty, only if its a Zero charger, which is tested and designed not to do this. That's why either you should get a Zero brand charger, or one that has been tested and designed to work with the Zero and proven not to cause damage like the ones from Hollywood Electrics.
If instead of Ford motor oil you used 5 quarts of cooking oil and your engine seized, ford would not cover it.
If you bought RAM from ebay that was a brand you never heard of, and it shorted your mother board it would not be covered
An example is about 8 years ago with Verizon flip phones, people would buy cheap wall replacement chargers, and the batteries would over 4 months swell, pop the case off the back, and the battery would get scorching hot and lose all talk time capacity.
The cheap Chinese charge cords would charge the battery too fast, overheat and damage it. Verizon did not warranty the batteries, instead they included notes to only use Verizon brand chargers.
If no damage occurs, you can use what ever charger you want, but if you make your own and you blow up al the boards from a voltage spike, this is not Zero's fault. Unless you are a power electronics technician, I would only use chargers from Zero or Hollywood Electrics for now until even more fail safes are put in place like the phone manufacturers use today. There are too many ways a simple mistake with a common server meanwell powersupply like I've seen on some DIY threads here can cause damage to the bike if the connection procedure isn't done properly each time and that would be to precharge the capacitors before connecting to the bike if the bike is on, or only connecting if the bike is off and the onboard charger is NOT plugged in, and then letting the Sevcon slowly precharge the caps in the accessory charger. The charge fuse was designed to protect the bike in a strange emergency, but never intended to be needed, so its location and design is built into the harness and the whole bike harness has to be replaced, or the harness has to be hacked with a knife and then for sure the warranty is invalid and it is no longer factory sealed. And with testing the Supercharger V1 over a year ago, one of the things that took so long was figuring out the conditions that caused the contactor to open, because when it did, the high voltage spike killed BMS's, Main Bike Boards, and we even killed Brandon's sevcon and he had to buy another and have Hollywood commission and program it for his motor offset. These are all things that took a lot of testing to figure out and build protections for.
Ask Doug S on this forum, if a charger isn't connected properly to the bike, it will in fact break the bike! His bike had to get shipped back to the factory last year for component replacement because of a 3rd party charger that had an error getting hooked up. It does happen and Doug is an Electrical Engineer with 30 years experience. But he wasn't privilege to the Zero systems and their tolerances, and to be honest, no one on this forum is, so it is advised against unless you are ok making a very expensive mistake.
Bottom line stick to the Zero or Hollywood Electrics tested chargers for now. Some may say 'I can do it cheaper myself or from somewhere else', but remember, the Hollywood Electrics name being attached to something means its been designed and tested many times to work with a Zero. There is a very important quality, assurance and peace of mind that comes with that.