The T069 and T088 ink cartridges for Epson Printer is compatible some time,but they still have some differences detailed .

The T069 series cartridges 7ml ink:
The T069120 ink cartridge is what Epson ships you with the printer (in most cases).  Epson refers to it as the “moderate use” inkjet cartridge.  You may have seen this as an option on the sticker inside the printer that tells you what cartridges to use in your printer.  It is important to note that if you can find these cartridges for half what the T068 series cartridges cost, buy two (2) of these and you get more ink for your money.  Comes in black T069120, cyan T069220, magenta T069320, and yellow T069420.
T069 series will work in the following printers: Epson Stylus CX5000, CX6000, CX7000F, CX8400, CX9400Fax, CX9475Fax, NX300, NX400, C120, WorkForce 500, WorkForce 600, WorkForce 30, WorkForce 40 inkjet printers. ** C120 CANNOT use the T069120 black.  Can use the color T069 series.

The T088 series cartridges 3ml ink:
The T088 series of cartridges are a joke.  They are the same shape and size as the above mentioned cartridges, but they contain a measly 3ml of ink.  If you own a printer that uses these cartridges exclusively, get rid of it (CX4400, CX4450).  If you don’t have to purchase these cartridges, don’t.
Designed for the low end consumer models Epson Stylus CX4400, CX4450, CX7400, CX7450. ** Sold exclusively through big box retail.
The image below was obtained by (1) cracking open the cartridge case, (2) removing the black tape that covered the viewable clear plastic coating.  This procedure turned out to be very difficult; it took us several tries.  These cartridges do not use a sponge to distribute the ink.  Rather, Epson uses a multi-chambered system that sends ink to the nozzle from two different chambers, and as you will notice not all the chambers contain ink.  This makes refilling almost impossible, and not very desirable.  Notice all the air-space you also pay for with the cartridge.