How big is this network? Do you use multiple routers or multiple IP subnets on your network? If not, then I recommend using IP "reservations" instead of Static IP assignments. These are similar functions with similar results, but definitely different.
The reason your issues happens is because after a power outage (or recycling of router), when using "Dynamic Host Configuration Protocol (DHCP)" (as most users do), new IP addresses are assigned on a first come first serve basis. So if Printer C is first to connect after power is restored, it will get the first IP assignment. After the next outage, if Printer E is first, it gets the first assignment and all the other devices "shift".
I live in
Tornado Alley so this was really a pain here. Even though all my computers and my network is supported by good UPSs, long-duration outages are not uncommon. So, once the UPS supporting my network runs out of battery, I would frequently have to configure my computers to access the networked printers via a different IP address. Not fun.
Static assignments will work but unlike the others, I do NOT recommend using Static IP assignments - except for file servers. To assign a Static IP, in some cases it must be done manually on each device, as well as in the router. That is, you have to run around the building and go into the menu system of each printer, each computer, each NAS, etc. access the NICs configuration menu, and manually set an IP address. What a pain - especially if you have many different devices.
The much easier (IMO) and definitely much faster approach is to set up a "DHCP Reservation" address. It is much easier because you do it all in your router's admin menu. And it is MUCH FASTER because you do it in your router's admin menu for
every device you want to assign the same IP address. You don't need to run around the building to every device, navigate a bunch of different menu systems, then figure out to assign that address.
It is also MUCH EASIER because you can easily see in that one menu system, which IP addresses you have used. Therefore, it is much easier to keep track of what IP address you assigned to which device. Even if the printer is taken off line, you can still see what IP address you assigned to it in your router's admin menu. Nice! :)
Note that different routers may use slightly different terminology for this feature. Log into your router's admin menu and look around. In my Netgear Nighthawk router's admin menu, I go to Advanced > Setup > LAN Setup. From there, there is a section called "Address Reservation". If the device is already connected, it is as simple as selecting it and setting the address. If not currently connected, you can manually enter the MAC Address and assign an IP address. Piece of case.
The way it works from then on is when the device attempts to connect to your network, the router sees the MAC address, then assigns the "reserved" IP address to it. Done! No other device can ever have it - unless
you assigned a Static IP address to it too. Then "conflicts" happen. Not good.
See:
Difference between static IP and DHCP reservation
