Yep, the initial powerplant upgrades you can find near liberty have pretty low regeneration rates. You aren't limited to the "upgrade mk" type powerplants, you know. There are also the block series of powerplants, as well as powerplants that come with the ships. Once you get past Liberty space, the variety you can choose from keeps increasing
Sometimes it's worth going to the ship dealer and click on purchase ship but don't actually buy it. When he's showing you the ship and what items to transfer, just look at the ship's powerplant and other stuff. If you like the equipment but not the ship itself, you can buy the ship, then re-buy your previous ship while transferring the powerplant and other goodies you want to keep from the new ship. Make sure you have enough money though.
Note that powerplants take up cargo space -- once I tried to transfer a really nice supercharged block but my new ship couldn't fit it onboard, heh. Also, you can't transfer engines so if you find a place selling one you like (e.g. an upgrade mk 3 or something), then remember that place cause when you buy a new ship you get new engines and can't transfer the old ones, so you have to go re-buy the upgrades. Lastly, if a ship has multiple engines mounted, don't try to upgrade cause if you unmount any of them, you can't re-mount extra engines (the game only allows you to have one).
It's fun hunting around to find the most suitable powerplant your ship can mount
" In Defeat, Malice; In Victory, Revenge! "